Auto merge of #24677 - jdm:iframe-sizing-cleanup, r=asajeffrey

Ensure all iframes are sized correctly at creation

Following in the path of #22395, these commits serve several purposes:
* prevent layout instability early during iframe loads caused by a succession of resize events
* reduce the complexity of determining what actual DPI and initial window size values are being used at startup
* ensure that all documents have a correct initial viewport size at creation

These changes fix problems that were exposed by the changes in #24462 but are independent of that PR.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

3 files changed, 10 insertions, 1 deletions

diff --git a/components/script_layout_interface/Cargo.toml b/components/script_layout_interface/Cargo.toml
index 8ad33fc7d43..2e436761dc8 100644
--- a/components/script_layout_interface/Cargo.toml
+++ b/components/script_layout_interface/Cargo.toml
@@ -33,4 +33,5 @@ servo_arc = {path = "../servo_arc"}
 servo_atoms = {path = "../atoms"}
 servo_url = {path = "../url"}
 style = {path = "../style", features = ["servo"]}
+style_traits = {path = "../style_traits", features = ["servo"]}
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
diff --git a/components/script_layout_interface/message.rs b/components/script_layout_interface/message.rs
index 01a589d53cb..fb2bac65d07 100644
--- a/components/script_layout_interface/message.rs
+++ b/components/script_layout_interface/message.rs
@@ -10,7 +10,7 @@ use euclid::default::{Point2D, Rect};
 use gfx_traits::Epoch;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use metrics::PaintTimeMetrics;
-use msg::constellation_msg::{BackgroundHangMonitorRegister, PipelineId};
+use msg::constellation_msg::{BackgroundHangMonitorRegister, BrowsingContextId, PipelineId};
 use net_traits::image_cache::ImageCache;
 use profile_traits::mem::ReportsChan;
 use script_traits::Painter;
@@ -128,6 +128,7 @@ pub enum QueryMsg {
     ResolvedStyleQuery(TrustedNodeAddress, Option<PseudoElement>, PropertyId),
     StyleQuery(TrustedNodeAddress),
     ElementInnerTextQuery(TrustedNodeAddress),
+    InnerWindowDimensionsQuery(BrowsingContextId),
 }
 
 /// Any query to perform with this reflow.
@@ -147,6 +148,7 @@ impl ReflowGoal {
             ReflowGoal::LayoutQuery(ref querymsg, _) => match *querymsg {
                 QueryMsg::NodesFromPointQuery(..) |
                 QueryMsg::TextIndexQuery(..) |
+                QueryMsg::InnerWindowDimensionsQuery(_) |
                 QueryMsg::ElementInnerTextQuery(_) => true,
                 QueryMsg::ContentBoxQuery(_) |
                 QueryMsg::ContentBoxesQuery(_) |
@@ -176,6 +178,7 @@ impl ReflowGoal {
                 QueryMsg::NodeScrollIdQuery(_) |
                 QueryMsg::ResolvedStyleQuery(..) |
                 QueryMsg::OffsetParentQuery(_) |
+                QueryMsg::InnerWindowDimensionsQuery(_) |
                 QueryMsg::StyleQuery(_) => false,
             },
         }
@@ -227,4 +230,5 @@ pub struct LayoutThreadInit {
     pub image_cache: Arc<dyn ImageCache>,
     pub paint_time_metrics: PaintTimeMetrics,
     pub layout_is_busy: Arc<AtomicBool>,
+    pub window_size: WindowSizeData,
 }
diff --git a/components/script_layout_interface/rpc.rs b/components/script_layout_interface/rpc.rs
index 95d25082ed8..19da8fa6afc 100644
--- a/components/script_layout_interface/rpc.rs
+++ b/components/script_layout_interface/rpc.rs
@@ -4,9 +4,11 @@
 
 use app_units::Au;
 use euclid::default::Rect;
+use euclid::Size2D;
 use script_traits::UntrustedNodeAddress;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
+use style_traits::CSSPixel;
 use webrender_api::ExternalScrollId;
 
 /// Synchronous messages that script can send to layout.
@@ -39,6 +41,8 @@ pub trait LayoutRPC {
     fn nodes_from_point_response(&self) -> Vec<UntrustedNodeAddress>;
     /// Query layout to get the inner text for a given element.
     fn element_inner_text(&self) -> String;
+    /// Get the dimensions of an iframe's inner window.
+    fn inner_window_dimensions(&self) -> Option<Size2D<f32, CSSPixel>>;
 }
 
 pub struct ContentBoxResponse(pub Option<Rect<Au>>);