Auto merge of #20307 - csmoe:measure_query_time, r=jdm

Measure time required before a layout query is serviced by the layout thread

<!-- Please describe your changes on the following line: -->

- [X] extract QueryMsg from ReflowGoal
- [X] introduce QueryMsg timestamp

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [x] These changes fix #19795 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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8 files changed, 218 insertions, 156 deletions

diff --git a/Cargo.lock b/Cargo.lock
index cf3c9006ef5..4652855608e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1170,6 +1170,11 @@ dependencies = [
 ]
 
 [[package]]
+name = "histogram"
+version = "0.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "html5ever"
 version = "0.22.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1443,6 +1448,7 @@ dependencies = [
  "fnv 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "gfx 0.0.1",
  "gfx_traits 0.0.1",
+ "histogram 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "html5ever 0.22.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "layout 0.0.1",
@@ -1471,6 +1477,7 @@ dependencies = [
  "servo_url 0.0.1",
  "style 0.0.1",
  "style_traits 0.0.1",
+ "time 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.57.0 (git+https://github.com/servo/webrender)",
 ]
 
@@ -2563,6 +2570,7 @@ dependencies = [
  "servo_atoms 0.0.1",
  "servo_url 0.0.1",
  "style 0.0.1",
+ "time 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.57.0 (git+https://github.com/servo/webrender)",
 ]
 
@@ -3847,6 +3855,7 @@ dependencies = [
 "checksum harfbuzz-sys 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)" = "52aa65c5649a0a2f1b27ab30093b3cc84681e17ddb552267e21948c5a6fa6b05"
 "checksum heartbeats-simple 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9ad003ce233955e9d95f2c69cde84e68302ba9ba4a673d351c9bff93c738aadc"
 "checksum heartbeats-simple-sys 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e1a408c0011427cc0e0049f7861c70377819aedfc006e8c901b1c70fd98fb1a4"
+"checksum histogram 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)" = "1bdcec4094c1ca961b685384ea7af76af5718230b3f34657d1a71fd2dcf4cc9d"
 "checksum html5ever 0.22.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e579ac8647178ab915d400d7d22938bda5cd351c6c62e1c294d56884ccfc75fe"
 "checksum httparse 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a6e7a63e511f9edffbab707141fbb8707d1a3098615fb2adbd5769cdfcc9b17d"
 "checksum hyper 0.10.13 (registry+https://github.com/rust-lang/crates.io-index)" = "368cb56b2740ebf4230520e2b90ebb0461e69034d85d1945febd9b3971426db2"
diff --git a/components/layout_thread/Cargo.toml b/components/layout_thread/Cargo.toml
index f7cffec344e..e7c54e353df 100644
--- a/components/layout_thread/Cargo.toml
+++ b/components/layout_thread/Cargo.toml
@@ -19,6 +19,7 @@ euclid = "0.17"
 fnv = "1.0"
 gfx = {path = "../gfx"}
 gfx_traits = {path = "../gfx_traits"}
+histogram = "0.6.8"
 html5ever = "0.22"
 ipc-channel = "0.10"
 layout = {path = "../layout"}
@@ -26,6 +27,7 @@ layout_traits = {path = "../layout_traits"}
 lazy_static = "1"
 libc = "0.2"
 log = "0.3.5"
+time = "0.1.17"
 malloc_size_of = { path = "../malloc_size_of" }
 metrics = {path = "../metrics"}
 msg = {path = "../msg"}
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 2ce013f658c..cdfa0f092c2 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -13,6 +13,7 @@ extern crate euclid;
 extern crate fnv;
 extern crate gfx;
 extern crate gfx_traits;
+extern crate histogram;
 #[macro_use]
 extern crate html5ever;
 extern crate ipc_channel;
@@ -46,6 +47,7 @@ extern crate servo_geometry;
 extern crate servo_url;
 extern crate style;
 extern crate style_traits;
+extern crate time as std_time;
 extern crate webrender_api;
 
 mod dom_wrapper;
@@ -60,6 +62,7 @@ use gfx::font;
 use gfx::font_cache_thread::FontCacheThread;
 use gfx::font_context;
 use gfx_traits::{Epoch, node_id_from_scroll_id};
+use histogram::Histogram;
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
 use ipc_channel::router::ROUTER;
 use layout::animation;
@@ -94,7 +97,7 @@ use profile_traits::mem::{self, Report, ReportKind, ReportsChan};
 use profile_traits::time::{self, TimerMetadata, profile};
 use profile_traits::time::{TimerMetadataFrameType, TimerMetadataReflowType};
 use script_layout_interface::message::{Msg, NewLayoutThreadInfo, NodesFromPointQueryType, Reflow};
-use script_layout_interface::message::{ReflowComplete, ReflowGoal, ScriptReflow};
+use script_layout_interface::message::{ReflowComplete, QueryMsg, ReflowGoal, ScriptReflow};
 use script_layout_interface::rpc::{LayoutRPC, StyleResponse, OffsetParentResponse};
 use script_layout_interface::rpc::TextIndexResponse;
 use script_layout_interface::wrapper_traits::LayoutNode;
@@ -260,6 +263,9 @@ pub struct LayoutThread {
 
     /// Paint time metrics.
     paint_time_metrics: PaintTimeMetrics,
+
+    /// The time a layout query has waited before serviced by layout thread.
+    layout_query_waiting_time: Histogram,
 }
 
 impl LayoutThreadFactory for LayoutThread {
@@ -332,6 +338,12 @@ impl Deref for ScriptReflowResult {
     }
 }
 
+impl DerefMut for ScriptReflowResult {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.script_reflow
+    }
+}
+
 impl ScriptReflowResult {
     fn new(script_reflow: ScriptReflow) -> ScriptReflowResult {
         ScriptReflowResult {
@@ -541,6 +553,7 @@ impl LayoutThread {
                 },
             layout_threads: layout_threads,
             paint_time_metrics: paint_time_metrics,
+            layout_query_waiting_time: Histogram::new(),
         }
     }
 
@@ -858,6 +871,16 @@ impl LayoutThread {
         // Drop the root flow explicitly to avoid holding style data, such as
         // rule nodes.  The `Stylist` checks when it is dropped that all rule
         // nodes have been GCed, so we want drop anyone who holds them first.
+        let waiting_time_min = self.layout_query_waiting_time.minimum().unwrap_or(0);
+        let waiting_time_max = self.layout_query_waiting_time.maximum().unwrap_or(0);
+        let waiting_time_mean = self.layout_query_waiting_time.mean().unwrap_or(0);
+        let waiting_time_stddev = self.layout_query_waiting_time.stddev().unwrap_or(0);
+        debug!("layout: query waiting time: min: {}, max: {}, mean: {}, standard_deviation: {}",
+               waiting_time_min,
+               waiting_time_max,
+               waiting_time_mean,
+               waiting_time_stddev);
+
         self.root_flow.borrow_mut().take();
         // Drop the rayon threadpool if present.
         let _ = self.parallel_traversal.take();
@@ -1078,43 +1101,51 @@ impl LayoutThread {
 
         let mut rw_data = possibly_locked_rw_data.lock();
 
+        // Record the time that layout query has been waited.
+        let now = std_time::precise_time_ns();
+        if let ReflowGoal::LayoutQuery(_, timestamp) = data.reflow_goal {
+            self.layout_query_waiting_time.increment(now - timestamp).expect("layout: wrong layout query timestamp");
+        };
+
         let element = match document.root_element() {
             None => {
                 // Since we cannot compute anything, give spec-required placeholders.
                 debug!("layout: No root node: bailing");
                 match data.reflow_goal {
-                    ReflowGoal::ContentBoxQuery(_) => {
-                        rw_data.content_box_response = None;
-                    },
-                    ReflowGoal::ContentBoxesQuery(_) => {
-                        rw_data.content_boxes_response = Vec::new();
-                    },
-                    ReflowGoal::NodesFromPointQuery(..) => {
-                        rw_data.nodes_from_point_response = Vec::new();
-                    },
-                    ReflowGoal::NodeGeometryQuery(_) => {
-                        rw_data.client_rect_response = Rect::zero();
-                    },
-                    ReflowGoal::NodeScrollGeometryQuery(_) => {
-                        rw_data.scroll_area_response = Rect::zero();
-                    },
-                    ReflowGoal::NodeScrollIdQuery(_) => {
-                        rw_data.scroll_id_response = None;
-                    },
-                    ReflowGoal::ResolvedStyleQuery(_, _, _) => {
-                        rw_data.resolved_style_response = String::new();
-                    },
-                    ReflowGoal::OffsetParentQuery(_) => {
-                        rw_data.offset_parent_response = OffsetParentResponse::empty();
-                    },
-                    ReflowGoal::StyleQuery(_) => {
-                        rw_data.style_response = StyleResponse(None);
-                    },
-                    ReflowGoal::TextIndexQuery(..) => {
-                        rw_data.text_index_response = TextIndexResponse(None);
-                    }
-                    ReflowGoal::ElementInnerTextQuery(_) => {
-                        rw_data.element_inner_text_response = String::new();
+                    ReflowGoal::LayoutQuery(ref query_msg, _) => match query_msg {
+                        &QueryMsg::ContentBoxQuery(_) => {
+                            rw_data.content_box_response = None;
+                        },
+                        &QueryMsg::ContentBoxesQuery(_) => {
+                            rw_data.content_boxes_response = Vec::new();
+                        },
+                        &QueryMsg::NodesFromPointQuery(..) => {
+                            rw_data.nodes_from_point_response = Vec::new();
+                        },
+                        &QueryMsg::NodeGeometryQuery(_) => {
+                            rw_data.client_rect_response = Rect::zero();
+                        },
+                        &QueryMsg::NodeScrollGeometryQuery(_) => {
+                            rw_data.scroll_area_response = Rect::zero();
+                        },
+                        &QueryMsg::NodeScrollIdQuery(_) => {
+                            rw_data.scroll_id_response = None;
+                        },
+                        &QueryMsg::ResolvedStyleQuery(_, _, _) => {
+                            rw_data.resolved_style_response = String::new();
+                        },
+                        &QueryMsg::OffsetParentQuery(_) => {
+                            rw_data.offset_parent_response = OffsetParentResponse::empty();
+                        },
+                        &QueryMsg::StyleQuery(_) => {
+                            rw_data.style_response = StyleResponse(None);
+                        },
+                        &QueryMsg::TextIndexQuery(..) => {
+                            rw_data.text_index_response = TextIndexResponse(None);
+                        }
+                        &QueryMsg::ElementInnerTextQuery(_) => {
+                            rw_data.element_inner_text_response = String::new();
+                        },
                     },
                     ReflowGoal::Full | ReflowGoal:: TickAnimations => {}
                 }
@@ -1355,80 +1386,82 @@ impl LayoutThread {
         };
         let root_flow = FlowRef::deref_mut(&mut root_flow);
         match *reflow_goal {
-            ReflowGoal::ContentBoxQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.content_box_response = process_content_box_request(node, root_flow);
-            },
-            ReflowGoal::ContentBoxesQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.content_boxes_response = process_content_boxes_request(node, root_flow);
-            },
-            ReflowGoal::TextIndexQuery(node, point_in_node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                let opaque_node = node.opaque();
-                let point_in_node = Point2D::new(
-                    Au::from_f32_px(point_in_node.x),
-                    Au::from_f32_px(point_in_node.y)
-                );
-                rw_data.text_index_response = TextIndexResponse(
-                    rw_data.indexable_text.text_index(opaque_node, point_in_node)
-                );
-            },
-            ReflowGoal::NodeGeometryQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.client_rect_response = process_node_geometry_request(node, root_flow);
-            },
-            ReflowGoal::NodeScrollGeometryQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.scroll_area_response = process_node_scroll_area_request(node, root_flow);
-            },
-            ReflowGoal::NodeScrollIdQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.scroll_id_response = Some(process_node_scroll_id_request(self.id, node));
-            },
-            ReflowGoal::ResolvedStyleQuery(node, ref pseudo, ref property) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.resolved_style_response =
-                    process_resolved_style_request(context,
-                                                   node,
-                                                   pseudo,
-                                                   property,
-                                                   root_flow);
-            },
-            ReflowGoal::OffsetParentQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.offset_parent_response = process_offset_parent_query(node, root_flow);
-            },
-            ReflowGoal::StyleQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.style_response = process_style_query(node);
-            },
-            ReflowGoal::NodesFromPointQuery(client_point, ref reflow_goal) => {
-                let mut flags = match reflow_goal {
-                    &NodesFromPointQueryType::Topmost => webrender_api::HitTestFlags::empty(),
-                    &NodesFromPointQueryType::All => webrender_api::HitTestFlags::FIND_ALL,
-                };
+            ReflowGoal::LayoutQuery(ref querymsg, _) => match querymsg {
+                &QueryMsg::ContentBoxQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.content_box_response = process_content_box_request(node, root_flow);
+                },
+                &QueryMsg::ContentBoxesQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.content_boxes_response = process_content_boxes_request(node, root_flow);
+                },
+                &QueryMsg::TextIndexQuery(node, point_in_node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    let opaque_node = node.opaque();
+                    let point_in_node = Point2D::new(
+                        Au::from_f32_px(point_in_node.x),
+                        Au::from_f32_px(point_in_node.y)
+                    );
+                    rw_data.text_index_response = TextIndexResponse(
+                        rw_data.indexable_text.text_index(opaque_node, point_in_node)
+                    );
+                },
+                &QueryMsg::NodeGeometryQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.client_rect_response = process_node_geometry_request(node, root_flow);
+                },
+                &QueryMsg::NodeScrollGeometryQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.scroll_area_response = process_node_scroll_area_request(node, root_flow);
+                },
+                &QueryMsg::NodeScrollIdQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.scroll_id_response = Some(process_node_scroll_id_request(self.id, node));
+                },
+                &QueryMsg::ResolvedStyleQuery(node, ref pseudo, ref property) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.resolved_style_response =
+                        process_resolved_style_request(context,
+                                                       node,
+                                                       pseudo,
+                                                       property,
+                                                       root_flow);
+                },
+                &QueryMsg::OffsetParentQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.offset_parent_response = process_offset_parent_query(node, root_flow);
+                },
+                &QueryMsg::StyleQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.style_response = process_style_query(node);
+                },
+                &QueryMsg::NodesFromPointQuery(client_point, ref reflow_goal) => {
+                    let mut flags = match reflow_goal {
+                        &NodesFromPointQueryType::Topmost => webrender_api::HitTestFlags::empty(),
+                        &NodesFromPointQueryType::All => webrender_api::HitTestFlags::FIND_ALL,
+                    };
 
-                // The point we get is not relative to the entire WebRender scene, but to this
-                // particular pipeline, so we need to tell WebRender about that.
-                flags.insert(webrender_api::HitTestFlags::POINT_RELATIVE_TO_PIPELINE_VIEWPORT);
+                    // The point we get is not relative to the entire WebRender scene, but to this
+                    // particular pipeline, so we need to tell WebRender about that.
+                    flags.insert(webrender_api::HitTestFlags::POINT_RELATIVE_TO_PIPELINE_VIEWPORT);
 
-                let client_point = webrender_api::WorldPoint::from_untyped(&client_point);
-                let results = self.webrender_api.hit_test(
-                    self.webrender_document,
-                    Some(self.id.to_webrender()),
-                    client_point,
-                    flags
-                );
+                    let client_point = webrender_api::WorldPoint::from_untyped(&client_point);
+                    let results = self.webrender_api.hit_test(
+                        self.webrender_document,
+                        Some(self.id.to_webrender()),
+                        client_point,
+                        flags
+                    );
 
-                rw_data.nodes_from_point_response = results.items.iter()
-                   .map(|item| UntrustedNodeAddress(item.tag.0 as *const c_void))
-                   .collect()
-            },
-            ReflowGoal::ElementInnerTextQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.element_inner_text_response =
-                    process_element_inner_text_query(node, &rw_data.indexable_text);
+                    rw_data.nodes_from_point_response = results.items.iter()
+                       .map(|item| UntrustedNodeAddress(item.tag.0 as *const c_void))
+                       .collect()
+                },
+                &QueryMsg::ElementInnerTextQuery(node) => {
+                    let node = unsafe { ServoLayoutNode::new(&node) };
+                    rw_data.element_inner_text_response =
+                        process_element_inner_text_query(node, &rw_data.indexable_text);
+                },
             },
             ReflowGoal::Full | ReflowGoal::TickAnimations => {}
         }
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index b1cee370bfe..01b9a13ba40 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -109,7 +109,7 @@ use num_traits::ToPrimitive;
 use profile_traits::ipc;
 use profile_traits::time::{TimerMetadata, TimerMetadataFrameType, TimerMetadataReflowType};
 use ref_slice::ref_slice;
-use script_layout_interface::message::{Msg, NodesFromPointQueryType, ReflowGoal};
+use script_layout_interface::message::{Msg, NodesFromPointQueryType, QueryMsg, ReflowGoal};
 use script_runtime::{CommonScriptMsg, ScriptThreadEventCategory};
 use script_thread::{MainThreadScriptMsg, ScriptThread};
 use script_traits::{AnimationState, DocumentActivity, MouseButton, MouseEventType};
@@ -1969,8 +1969,7 @@ impl Document {
                             client_point: &Point2D<f32>,
                             reflow_goal: NodesFromPointQueryType)
                             -> Vec<UntrustedNodeAddress> {
-        if !self.window.reflow(ReflowGoal::NodesFromPointQuery(*client_point, reflow_goal),
-                               ReflowReason::Query) {
+        if !self.window.layout_reflow(QueryMsg::NodesFromPointQuery(*client_point, reflow_goal)) {
             return vec!();
         };
 
diff --git a/components/script/dom/htmlelement.rs b/components/script/dom/htmlelement.rs
index 021f25161b9..e28ff1053a2 100644
--- a/components/script/dom/htmlelement.rs
+++ b/components/script/dom/htmlelement.rs
@@ -32,10 +32,9 @@ use dom::node::{document_from_node, window_from_node};
 use dom::nodelist::NodeList;
 use dom::text::Text;
 use dom::virtualmethods::VirtualMethods;
-use dom::window::ReflowReason;
 use dom_struct::dom_struct;
 use html5ever::{LocalName, Prefix};
-use script_layout_interface::message::ReflowGoal;
+use script_layout_interface::message::QueryMsg;
 use std::collections::HashSet;
 use std::default::Default;
 use std::rc::Rc;
@@ -419,7 +418,7 @@ impl HTMLElementMethods for HTMLElement {
             return node.GetTextContent().unwrap();
         }
 
-        window.reflow(ReflowGoal::ElementInnerTextQuery(node.to_trusted_node_address()), ReflowReason::Query);
+        window.layout_reflow(QueryMsg::ElementInnerTextQuery(node.to_trusted_node_address()));
         DOMString::from(window.layout().element_inner_text())
     }
 
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 327e766e7fa..29ea1caf3f0 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -67,7 +67,7 @@ use profile_traits::ipc as ProfiledIpc;
 use profile_traits::mem::ProfilerChan as MemProfilerChan;
 use profile_traits::time::ProfilerChan as TimeProfilerChan;
 use script_layout_interface::{TrustedNodeAddress, PendingImageState};
-use script_layout_interface::message::{Msg, Reflow, ReflowGoal, ScriptReflow};
+use script_layout_interface::message::{Msg, Reflow, QueryMsg, ReflowGoal, ScriptReflow};
 use script_layout_interface::reporter::CSSErrorReporter;
 use script_layout_interface::rpc::{ContentBoxResponse, ContentBoxesResponse, LayoutRPC};
 use script_layout_interface::rpc::{NodeScrollIdResponse, ResolvedStyleResponse, TextIndexResponse};
@@ -1385,12 +1385,16 @@ impl Window {
         issued_reflow
     }
 
+    pub fn layout_reflow(&self, query_msg: QueryMsg) -> bool {
+        self.reflow(ReflowGoal::LayoutQuery(query_msg, time::precise_time_ns()), ReflowReason::Query)
+    }
+
     pub fn layout(&self) -> &LayoutRPC {
         &*self.layout_rpc
     }
 
     pub fn content_box_query(&self, content_box_request: TrustedNodeAddress) -> Option<Rect<Au>> {
-        if !self.reflow(ReflowGoal::ContentBoxQuery(content_box_request), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::ContentBoxQuery(content_box_request)) {
             return None;
         }
         let ContentBoxResponse(rect) = self.layout_rpc.content_box();
@@ -1398,7 +1402,7 @@ impl Window {
     }
 
     pub fn content_boxes_query(&self, content_boxes_request: TrustedNodeAddress) -> Vec<Rect<Au>> {
-        if !self.reflow(ReflowGoal::ContentBoxesQuery(content_boxes_request), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::ContentBoxesQuery(content_boxes_request)) {
             return vec![];
         }
         let ContentBoxesResponse(rects) = self.layout_rpc.content_boxes();
@@ -1406,14 +1410,14 @@ impl Window {
     }
 
     pub fn client_rect_query(&self, node_geometry_request: TrustedNodeAddress) -> Rect<i32> {
-        if !self.reflow(ReflowGoal::NodeGeometryQuery(node_geometry_request), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::NodeGeometryQuery(node_geometry_request)) {
             return Rect::zero();
         }
         self.layout_rpc.node_geometry().client_rect
     }
 
     pub fn scroll_area_query(&self, node: TrustedNodeAddress) -> Rect<i32> {
-        if !self.reflow(ReflowGoal::NodeScrollGeometryQuery(node), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::NodeScrollGeometryQuery(node)) {
             return Rect::zero();
         }
         self.layout_rpc.node_scroll_area().client_rect
@@ -1436,10 +1440,7 @@ impl Window {
         y_: f64,
         behavior: ScrollBehavior
     ) {
-        if !self.reflow(
-            ReflowGoal::NodeScrollIdQuery(node.to_trusted_node_address()),
-            ReflowReason::Query
-        ) {
+        if !self.layout_reflow(QueryMsg::NodeScrollIdQuery(node.to_trusted_node_address())) {
             return;
         }
 
@@ -1463,8 +1464,7 @@ impl Window {
                                 element: TrustedNodeAddress,
                                 pseudo: Option<PseudoElement>,
                                 property: PropertyId) -> DOMString {
-        if !self.reflow(ReflowGoal::ResolvedStyleQuery(element, pseudo, property),
-                        ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::ResolvedStyleQuery(element, pseudo, property)) {
             return DOMString::new();
         }
         let ResolvedStyleResponse(resolved) = self.layout_rpc.resolved_style();
@@ -1473,7 +1473,7 @@ impl Window {
 
     #[allow(unsafe_code)]
     pub fn offset_parent_query(&self, node: TrustedNodeAddress) -> (Option<DomRoot<Element>>, Rect<Au>) {
-        if !self.reflow(ReflowGoal::OffsetParentQuery(node), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::OffsetParentQuery(node)) {
             return (None, Rect::zero());
         }
 
@@ -1488,7 +1488,7 @@ impl Window {
     }
 
     pub fn style_query(&self, node: TrustedNodeAddress) -> Option<servo_arc::Arc<ComputedValues>> {
-        if !self.reflow(ReflowGoal::StyleQuery(node), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::StyleQuery(node)) {
             return None
         }
         self.layout_rpc.style().0
@@ -1499,7 +1499,7 @@ impl Window {
         node: TrustedNodeAddress,
         point_in_node: Point2D<f32>
     ) -> TextIndexResponse {
-        if !self.reflow(ReflowGoal::TextIndexQuery(node, point_in_node), ReflowReason::Query) {
+        if !self.layout_reflow(QueryMsg::TextIndexQuery(node, point_in_node)) {
             return TextIndexResponse(None);
         }
         self.layout_rpc.text_index()
@@ -1881,18 +1881,20 @@ fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal, reason: &Reflow
     let mut debug_msg = format!("**** pipeline={}", id);
     debug_msg.push_str(match *reflow_goal {
         ReflowGoal::Full => "\tFull",
-        ReflowGoal::ContentBoxQuery(_n) => "\tContentBoxQuery",
-        ReflowGoal::ContentBoxesQuery(_n) => "\tContentBoxesQuery",
-        ReflowGoal::NodesFromPointQuery(..) => "\tNodesFromPointQuery",
-        ReflowGoal::NodeGeometryQuery(_n) => "\tNodeGeometryQuery",
-        ReflowGoal::NodeScrollGeometryQuery(_n) => "\tNodeScrollGeometryQuery",
-        ReflowGoal::NodeScrollIdQuery(_n) => "\tNodeScrollIdQuery",
-        ReflowGoal::ResolvedStyleQuery(_, _, _) => "\tResolvedStyleQuery",
-        ReflowGoal::OffsetParentQuery(_n) => "\tOffsetParentQuery",
-        ReflowGoal::StyleQuery(_n) => "\tStyleQuery",
-        ReflowGoal::TextIndexQuery(..) => "\tTextIndexQuery",
         ReflowGoal::TickAnimations => "\tTickAnimations",
-        ReflowGoal::ElementInnerTextQuery(_) => "\tElementInnerTextQuery",
+        ReflowGoal::LayoutQuery(ref query_msg, _) => match query_msg {
+            &QueryMsg::ContentBoxQuery(_n) => "\tContentBoxQuery",
+            &QueryMsg::ContentBoxesQuery(_n) => "\tContentBoxesQuery",
+            &QueryMsg::NodesFromPointQuery(..) => "\tNodesFromPointQuery",
+            &QueryMsg::NodeGeometryQuery(_n) => "\tNodeGeometryQuery",
+            &QueryMsg::NodeScrollGeometryQuery(_n) => "\tNodeScrollGeometryQuery",
+            &QueryMsg::NodeScrollIdQuery(_n) => "\tNodeScrollIdQuery",
+            &QueryMsg::ResolvedStyleQuery(_, _, _) => "\tResolvedStyleQuery",
+            &QueryMsg::OffsetParentQuery(_n) => "\tOffsetParentQuery",
+            &QueryMsg::StyleQuery(_n) => "\tStyleQuery",
+            &QueryMsg::TextIndexQuery(..) => "\tTextIndexQuery",
+            &QueryMsg::ElementInnerTextQuery(_) => "\tElementInnerTextQuery",
+        },
     });
 
     debug_msg.push_str(match *reason {
diff --git a/components/script_layout_interface/Cargo.toml b/components/script_layout_interface/Cargo.toml
index 51afedae058..f662ced9a35 100644
--- a/components/script_layout_interface/Cargo.toml
+++ b/components/script_layout_interface/Cargo.toml
@@ -20,6 +20,7 @@ html5ever = "0.22"
 ipc-channel = "0.10"
 libc = "0.2"
 log = "0.3.5"
+time = "0.1.17"
 malloc_size_of = { path = "../malloc_size_of" }
 malloc_size_of_derive = { path = "../malloc_size_of_derive" }
 metrics = {path = "../metrics"}
diff --git a/components/script_layout_interface/message.rs b/components/script_layout_interface/message.rs
index ef408600270..ac52d9373ce 100644
--- a/components/script_layout_interface/message.rs
+++ b/components/script_layout_interface/message.rs
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use {OpaqueStyleAndLayoutData, TrustedNodeAddress, PendingImage};
+use {OpaqueStyleAndLayoutData, PendingImage, TrustedNodeAddress};
 use app_units::Au;
 use euclid::{Point2D, Rect};
 use gfx_traits::Epoch;
@@ -106,11 +106,8 @@ pub enum NodesFromPointQueryType {
     Topmost,
 }
 
-/// Any query to perform with this reflow.
 #[derive(Debug, PartialEq)]
-pub enum ReflowGoal {
-    Full,
-    TickAnimations,
+pub enum QueryMsg {
     ContentBoxQuery(TrustedNodeAddress),
     ContentBoxesQuery(TrustedNodeAddress),
     NodeScrollIdQuery(TrustedNodeAddress),
@@ -124,19 +121,33 @@ pub enum ReflowGoal {
     ElementInnerTextQuery(TrustedNodeAddress),
 }
 
+/// Any query to perform with this reflow.
+#[derive(Debug, PartialEq)]
+pub enum ReflowGoal {
+    Full,
+    TickAnimations,
+    LayoutQuery(QueryMsg, u64),
+}
+
 impl ReflowGoal {
     /// Returns true if the given ReflowQuery needs a full, up-to-date display list to
     /// be present or false if it only needs stacking-relative positions.
     pub fn needs_display_list(&self) -> bool {
         match *self {
-            ReflowGoal::NodesFromPointQuery(..) | ReflowGoal::TextIndexQuery(..) |
-            ReflowGoal::TickAnimations | ReflowGoal::ElementInnerTextQuery(_) |
-            ReflowGoal::Full => true,
-            ReflowGoal::ContentBoxQuery(_) | ReflowGoal::ContentBoxesQuery(_) |
-            ReflowGoal::NodeGeometryQuery(_) | ReflowGoal::NodeScrollGeometryQuery(_) |
-            ReflowGoal::NodeScrollIdQuery(_) |
-            ReflowGoal::ResolvedStyleQuery(..) | ReflowGoal::OffsetParentQuery(_) |
-            ReflowGoal::StyleQuery(_) => false,
+            ReflowGoal::Full | ReflowGoal::TickAnimations => true,
+            ReflowGoal::LayoutQuery(ref querymsg, _) => match querymsg {
+                &QueryMsg::NodesFromPointQuery(..) |
+                &QueryMsg::TextIndexQuery(..) |
+                &QueryMsg::ElementInnerTextQuery(_) => true,
+                &QueryMsg::ContentBoxQuery(_) |
+                &QueryMsg::ContentBoxesQuery(_) |
+                &QueryMsg::NodeGeometryQuery(_) |
+                &QueryMsg::NodeScrollGeometryQuery(_) |
+                &QueryMsg::NodeScrollIdQuery(_) |
+                &QueryMsg::ResolvedStyleQuery(..) |
+                &QueryMsg::OffsetParentQuery(_) |
+                &QueryMsg::StyleQuery(_) => false,
+            },
         }
     }
 
@@ -144,14 +155,20 @@ impl ReflowGoal {
     /// false if a layout_thread display list is sufficient.
     pub fn needs_display(&self) -> bool {
         match *self {
-            ReflowGoal::StyleQuery(_)  | ReflowGoal::TextIndexQuery(..) |
-            ReflowGoal::ContentBoxQuery(_) | ReflowGoal::ContentBoxesQuery(_) |
-            ReflowGoal::NodeGeometryQuery(_) | ReflowGoal::NodeScrollGeometryQuery(_) |
-            ReflowGoal::NodeScrollIdQuery(_) | ReflowGoal::ResolvedStyleQuery(..) |
-            ReflowGoal::OffsetParentQuery(_) => false,
-            ReflowGoal::NodesFromPointQuery(..) | ReflowGoal::Full |
-            ReflowGoal::ElementInnerTextQuery(_) |
-            ReflowGoal::TickAnimations => true,
+            ReflowGoal::Full | ReflowGoal::TickAnimations => true,
+            ReflowGoal::LayoutQuery(ref querymsg, _) => match querymsg {
+                &QueryMsg::NodesFromPointQuery(..) |
+                &QueryMsg::TextIndexQuery(..) |
+                &QueryMsg::ElementInnerTextQuery(_) => true,
+                &QueryMsg::ContentBoxQuery(_) |
+                &QueryMsg::ContentBoxesQuery(_) |
+                &QueryMsg::NodeGeometryQuery(_) |
+                &QueryMsg::NodeScrollGeometryQuery(_) |
+                &QueryMsg::NodeScrollIdQuery(_) |
+                &QueryMsg::ResolvedStyleQuery(..) |
+                &QueryMsg::OffsetParentQuery(_) |
+                &QueryMsg::StyleQuery(_) => false,
+            },
         }
     }
 }