Excise SubpageId and use only PipelineIds

SubpageId was originally introduced in 2013 to help iframes keep track of
their associated (children) pipelines. However, since each pipeline
already has a PipelineId, and those are unique, those are sufficient
to keep track of children.

7 files changed, 74 insertions, 121 deletions

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index fae24096bac..8125013a960 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -57,7 +57,7 @@ use js::jsapi::{GCTraceKindToAscii, Heap, JSObject, JSTracer, TraceKind};
 use js::jsval::JSVal;
 use js::rust::Runtime;
 use libc;
-use msg::constellation_msg::{FrameType, PipelineId, ReferrerPolicy, SubpageId, WindowSizeType};
+use msg::constellation_msg::{FrameType, PipelineId, ReferrerPolicy, WindowSizeType};
 use net_traits::{Metadata, NetworkError, ResourceThreads};
 use net_traits::filemanager_thread::RelativePos;
 use net_traits::image::base::{Image, ImageMetadata};
@@ -308,7 +308,7 @@ no_jsmanaged_fields!(PropertyDeclarationBlock);
 no_jsmanaged_fields!(HashSet<T>);
 // These three are interdependent, if you plan to put jsmanaged data
 // in one of these make sure it is propagated properly to containing structs
-no_jsmanaged_fields!(FrameType, SubpageId, WindowSizeData, WindowSizeType, PipelineId);
+no_jsmanaged_fields!(FrameType, WindowSizeData, WindowSizeType, PipelineId);
 no_jsmanaged_fields!(TimerEventId, TimerSource);
 no_jsmanaged_fields!(WorkerId);
 no_jsmanaged_fields!(QuirksMode);
diff --git a/components/script/dom/browsingcontext.rs b/components/script/dom/browsingcontext.rs
index dad7dfa3b91..02d153296ae 100644
--- a/components/script/dom/browsingcontext.rs
+++ b/components/script/dom/browsingcontext.rs
@@ -26,7 +26,7 @@ use js::jsapi::{JS_GetOwnPropertyDescriptorById, JS_HasPropertyById};
 use js::jsapi::{MutableHandle, MutableHandleObject, MutableHandleValue};
 use js::jsapi::{ObjectOpResult, PropertyDescriptor};
 use js::jsval::{UndefinedValue, PrivateValue};
-use msg::constellation_msg::{PipelineId, SubpageId};
+use msg::constellation_msg::PipelineId;
 use std::cell::Cell;
 use url::Url;
 
@@ -160,10 +160,10 @@ impl BrowsingContext {
         self.children.borrow_mut().push(JS::from_ref(&context));
     }
 
-    pub fn find_child_by_subpage(&self, subpage_id: SubpageId) -> Option<Root<Window>> {
+    pub fn find_child_by_id(&self, pipeline_id: PipelineId) -> Option<Root<Window>> {
         self.children.borrow().iter().find(|context| {
             let window = context.active_window();
-            window.subpage() == Some(subpage_id)
+            window.pipeline_id() == pipeline_id
         }).map(|context| context.active_window())
     }
 
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index a43194783a0..3436a4aaa0b 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -94,7 +94,7 @@ use js::jsapi::{JSContext, JSObject, JSRuntime};
 use js::jsapi::JS_GetRuntime;
 use msg::constellation_msg::{ALT, CONTROL, SHIFT, SUPER};
 use msg::constellation_msg::{Key, KeyModifiers, KeyState};
-use msg::constellation_msg::{PipelineId, ReferrerPolicy, SubpageId};
+use msg::constellation_msg::{PipelineId, ReferrerPolicy};
 use net_traits::{AsyncResponseTarget, IpcSend, PendingAsyncLoad};
 use net_traits::CookieSource::NonHTTP;
 use net_traits::CoreResourceMsg::{GetCookiesForUrl, SetCookiesForUrl};
@@ -1342,9 +1342,9 @@ impl Document {
 
     pub fn trigger_mozbrowser_event(&self, event: MozBrowserEvent) {
         if PREFS.is_mozbrowser_enabled() {
-            if let Some((parent_pipeline_id, subpage_id, _)) = self.window.parent_info() {
+            if let Some((parent_pipeline_id, _)) = self.window.parent_info() {
                 let event = ConstellationMsg::MozBrowserEvent(parent_pipeline_id,
-                                                              Some(subpage_id),
+                                                              Some(self.window.pipeline_id()),
                                                               event);
                 self.window.constellation_chan().send(event).unwrap();
             }
@@ -1581,15 +1581,7 @@ impl Document {
     }
 
     /// Find an iframe element in the document.
-    pub fn find_iframe(&self, subpage_id: SubpageId) -> Option<Root<HTMLIFrameElement>> {
-        self.upcast::<Node>()
-            .traverse_preorder()
-            .filter_map(Root::downcast::<HTMLIFrameElement>)
-            .find(|node| node.subpage_id() == Some(subpage_id))
-    }
-
-    /// Find an iframe element in the document.
-    pub fn find_iframe_by_pipeline(&self, pipeline: PipelineId) -> Option<Root<HTMLIFrameElement>> {
+    pub fn find_iframe(&self, pipeline: PipelineId) -> Option<Root<HTMLIFrameElement>> {
         self.upcast::<Node>()
             .traverse_preorder()
             .filter_map(Root::downcast::<HTMLIFrameElement>)
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index 051f7588687..220eb7d1c7c 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -38,7 +38,7 @@ use dom::window::{ReflowReason, Window};
 use ipc_channel::ipc;
 use js::jsapi::{JSAutoCompartment, JSContext, MutableHandleValue};
 use js::jsval::{NullValue, UndefinedValue};
-use msg::constellation_msg::{FrameType, LoadData, PipelineId, SubpageId, TraversalDirection};
+use msg::constellation_msg::{FrameType, LoadData, PipelineId, TraversalDirection};
 use net_traits::response::HttpsState;
 use script_layout_interface::message::ReflowQueryType;
 use script_traits::{IFrameLoadInfo, MozBrowserEvent, ScriptMsg as ConstellationMsg};
@@ -68,7 +68,6 @@ bitflags! {
 pub struct HTMLIFrameElement {
     htmlelement: HTMLElement,
     pipeline_id: Cell<Option<PipelineId>>,
-    subpage_id: Cell<Option<SubpageId>>,
     sandbox: MutNullableHeap<JS<DOMTokenList>>,
     sandbox_allowance: Cell<Option<SandboxAllowance>>,
     load_blocker: DOMRefCell<Option<LoadBlocker>>,
@@ -94,14 +93,11 @@ impl HTMLIFrameElement {
         }).unwrap_or_else(|| Url::parse("about:blank").unwrap())
     }
 
-    pub fn generate_new_subpage_id(&self) -> (SubpageId, Option<SubpageId>) {
-        self.pipeline_id.set(Some(PipelineId::new()));
-
-        let old_subpage_id = self.subpage_id.get();
-        let win = window_from_node(self);
-        let subpage_id = win.get_next_subpage_id();
-        self.subpage_id.set(Some(subpage_id));
-        (subpage_id, old_subpage_id)
+    pub fn generate_new_pipeline_id(&self) -> (Option<PipelineId>, PipelineId) {
+        let old_pipeline_id = self.pipeline_id.get();
+        let new_pipeline_id = PipelineId::new();
+        self.pipeline_id.set(Some(new_pipeline_id));
+        (old_pipeline_id, new_pipeline_id)
     }
 
     pub fn navigate_or_reload_child_browsing_context(&self, load_data: Option<LoadData>) {
@@ -126,16 +122,14 @@ impl HTMLIFrameElement {
         }
 
         let window = window_from_node(self);
-        let (new_subpage_id, old_subpage_id) = self.generate_new_subpage_id();
-        let new_pipeline_id = self.pipeline_id.get().unwrap();
+        let (old_pipeline_id, new_pipeline_id) = self.generate_new_pipeline_id();
         let private_iframe = self.privatebrowsing();
         let frame_type = if self.Mozbrowser() { FrameType::MozBrowserIFrame } else { FrameType::IFrame };
 
         let load_info = IFrameLoadInfo {
             load_data: load_data,
             parent_pipeline_id: window.pipeline_id(),
-            new_subpage_id: new_subpage_id,
-            old_subpage_id: old_subpage_id,
+            old_pipeline_id: old_pipeline_id,
             new_pipeline_id: new_pipeline_id,
             sandbox: sandboxed,
             is_private: private_iframe,
@@ -170,8 +164,7 @@ impl HTMLIFrameElement {
         }
     }
 
-    pub fn update_subpage_id(&self, new_subpage_id: SubpageId, new_pipeline_id: PipelineId) {
-        self.subpage_id.set(Some(new_subpage_id));
+    pub fn update_pipeline_id(&self, new_pipeline_id: PipelineId) {
         self.pipeline_id.set(Some(new_pipeline_id));
 
         let mut blocker = self.load_blocker.borrow_mut();
@@ -186,7 +179,6 @@ impl HTMLIFrameElement {
         HTMLIFrameElement {
             htmlelement: HTMLElement::new_inherited(localName, prefix, document),
             pipeline_id: Cell::new(None),
-            subpage_id: Cell::new(None),
             sandbox: Default::default(),
             sandbox_allowance: Cell::new(None),
             load_blocker: DOMRefCell::new(None),
@@ -208,11 +200,6 @@ impl HTMLIFrameElement {
         self.pipeline_id.get()
     }
 
-    #[inline]
-    pub fn subpage_id(&self) -> Option<SubpageId> {
-        self.subpage_id.get()
-    }
-
     pub fn change_visibility_status(&self, visibility: bool) {
         if self.visibility.get() != visibility {
             self.visibility.set(visibility);
@@ -270,11 +257,11 @@ impl HTMLIFrameElement {
     }
 
     pub fn get_content_window(&self) -> Option<Root<Window>> {
-        self.subpage_id.get().and_then(|subpage_id| {
+        self.pipeline_id.get().and_then(|pipeline_id| {
             let window = window_from_node(self);
             let window = window.r();
             let browsing_context = window.browsing_context();
-            browsing_context.find_child_by_subpage(subpage_id)
+            browsing_context.find_child_by_id(pipeline_id)
         })
     }
 
@@ -659,12 +646,11 @@ impl VirtualMethods for HTMLIFrameElement {
                 receiver.recv().unwrap()
             }
 
-            // Resetting the subpage id to None is required here so that
+            // Resetting the pipeline_id to None is required here so that
             // if this iframe is subsequently re-added to the document
             // the load doesn't think that it's a navigation, but instead
             // a new iframe. Without this, the constellation gets very
             // confused.
-            self.subpage_id.set(None);
             self.pipeline_id.set(None);
         }
     }
diff --git a/components/script/dom/servohtmlparser.rs b/components/script/dom/servohtmlparser.rs
index 548dad24dae..24a22be75dd 100644
--- a/components/script/dom/servohtmlparser.rs
+++ b/components/script/dom/servohtmlparser.rs
@@ -30,7 +30,7 @@ use hyper::header::ContentType;
 use hyper::mime::{Mime, SubLevel, TopLevel};
 use hyper_serde::Serde;
 use js::jsapi::JSTracer;
-use msg::constellation_msg::{PipelineId, SubpageId};
+use msg::constellation_msg::PipelineId;
 use net_traits::{AsyncResponseListener, Metadata, NetworkError};
 use network_listener::PreInvoke;
 use parse::{Parser, ParserRef, TrustedParser};
@@ -67,19 +67,16 @@ pub struct ParserContext {
     is_synthesized_document: bool,
     /// The pipeline associated with this document.
     id: PipelineId,
-    /// The subpage associated with this document.
-    subpage: Option<SubpageId>,
     /// The URL for this document.
     url: Url,
 }
 
 impl ParserContext {
-    pub fn new(id: PipelineId, subpage: Option<SubpageId>, url: Url) -> ParserContext {
+    pub fn new(id: PipelineId, url: Url) -> ParserContext {
         ParserContext {
             parser: None,
             is_synthesized_document: false,
             id: id,
-            subpage: subpage,
             url: url,
         }
     }
@@ -102,7 +99,6 @@ impl AsyncResponseListener for ParserContext {
         let content_type =
             metadata.clone().and_then(|meta| meta.content_type).map(Serde::into_inner);
         let parser = match ScriptThread::page_headers_available(&self.id,
-                                                                self.subpage.as_ref(),
                                                                 metadata) {
             Some(parser) => parser,
             None => return,
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index da8d9be0ead..f4efcd8dd76 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -51,7 +51,7 @@ use js::jsval::UndefinedValue;
 use js::rust::CompileOptionsWrapper;
 use js::rust::Runtime;
 use libc;
-use msg::constellation_msg::{FrameType, LoadData, PipelineId, SubpageId, WindowSizeType};
+use msg::constellation_msg::{FrameType, LoadData, PipelineId, WindowSizeType};
 use net_traits::ResourceThreads;
 use net_traits::bluetooth_thread::BluetoothMethodMsg;
 use net_traits::image_cache_thread::{ImageCacheChan, ImageCacheThread};
@@ -200,16 +200,14 @@ pub struct Window {
     /// page changes.
     devtools_wants_updates: Cell<bool>,
 
-    next_subpage_id: Cell<SubpageId>,
-
     /// Pending resize event, if any.
     resize_event: Cell<Option<(WindowSizeData, WindowSizeType)>>,
 
     /// Pipeline id associated with this page.
     id: PipelineId,
 
-    /// Subpage id associated with this page, if any.
-    parent_info: Option<(PipelineId, SubpageId, FrameType)>,
+    /// Parent id associated with this page, if any.
+    parent_info: Option<(PipelineId, FrameType)>,
 
     /// Global static data related to the DOM.
     dom_static: GlobalStaticData,
@@ -335,11 +333,7 @@ impl Window {
         self.id
     }
 
-    pub fn subpage(&self) -> Option<SubpageId> {
-        self.parent_info.map(|p| p.1)
-    }
-
-    pub fn parent_info(&self) -> Option<(PipelineId, SubpageId, FrameType)> {
+    pub fn parent_info(&self) -> Option<(PipelineId, FrameType)> {
         self.parent_info
     }
 
@@ -1492,13 +1486,6 @@ impl Window {
         WindowProxyHandler(self.dom_static.windowproxy_handler.0)
     }
 
-    pub fn get_next_subpage_id(&self) -> SubpageId {
-        let subpage_id = self.next_subpage_id.get();
-        let SubpageId(id_num) = subpage_id;
-        self.next_subpage_id.set(SubpageId(id_num + 1));
-        subpage_id
-    }
-
     pub fn get_pending_reflow_count(&self) -> u32 {
         self.pending_reflow_count.get()
     }
@@ -1612,7 +1599,7 @@ impl Window {
     // https://html.spec.whatwg.org/multipage/#top-level-browsing-context
     pub fn is_top_level(&self) -> bool {
         match self.parent_info {
-            Some((_, _, FrameType::IFrame)) => false,
+            Some((_, FrameType::IFrame)) => false,
             _ => true,
         }
     }
@@ -1676,7 +1663,7 @@ impl Window {
                timer_event_chan: IpcSender<TimerEvent>,
                layout_chan: Sender<Msg>,
                id: PipelineId,
-               parent_info: Option<(PipelineId, SubpageId, FrameType)>,
+               parent_info: Option<(PipelineId, FrameType)>,
                window_size: Option<WindowSizeData>)
                -> Root<Window> {
         let layout_rpc: Box<LayoutRPC> = {
@@ -1726,7 +1713,6 @@ impl Window {
             page_clip_rect: Cell::new(max_rect()),
             fragment_name: DOMRefCell::new(None),
             resize_event: Cell::new(None),
-            next_subpage_id: Cell::new(SubpageId(0)),
             layout_chan: layout_chan,
             layout_rpc: layout_rpc,
             window_size: Cell::new(window_size),
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 41f72d909cf..2e9bbf617f3 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -65,7 +65,7 @@ use js::jsval::UndefinedValue;
 use js::rust::Runtime;
 use mem::heap_size_of_self_and_children;
 use msg::constellation_msg::{FrameType, LoadData, PipelineId, PipelineNamespace};
-use msg::constellation_msg::{ReferrerPolicy, SubpageId, WindowSizeType};
+use msg::constellation_msg::{ReferrerPolicy, WindowSizeType};
 use net_traits::{AsyncResponseTarget, CoreResourceMsg, LoadConsumer, LoadContext, Metadata, ResourceThreads};
 use net_traits::{IpcSend, LoadData as NetLoadData};
 use net_traits::bluetooth_thread::BluetoothMethodMsg;
@@ -131,8 +131,8 @@ pub unsafe fn trace_thread(tr: *mut JSTracer) {
 struct InProgressLoad {
     /// The pipeline which requested this load.
     pipeline_id: PipelineId,
-    /// The parent pipeline and child subpage associated with this load, if any.
-    parent_info: Option<(PipelineId, SubpageId, FrameType)>,
+    /// The parent pipeline and frame type associated with this load, if any.
+    parent_info: Option<(PipelineId, FrameType)>,
     /// The current window size associated with this pipeline.
     window_size: Option<WindowSizeData>,
     /// Channel to the layout thread associated with this pipeline.
@@ -150,7 +150,7 @@ struct InProgressLoad {
 impl InProgressLoad {
     /// Create a new InProgressLoad object.
     fn new(id: PipelineId,
-           parent_info: Option<(PipelineId, SubpageId, FrameType)>,
+           parent_info: Option<(PipelineId, FrameType)>,
            layout_chan: Sender<message::Msg>,
            window_size: Option<WindowSizeData>,
            url: Url) -> InProgressLoad {
@@ -484,11 +484,11 @@ impl ScriptThreadFactory for ScriptThread {
 }
 
 impl ScriptThread {
-    pub fn page_headers_available(id: &PipelineId, subpage: Option<&SubpageId>, metadata: Option<Metadata>)
+    pub fn page_headers_available(id: &PipelineId, metadata: Option<Metadata>)
                                   -> Option<ParserRoot> {
         SCRIPT_THREAD_ROOT.with(|root| {
             let script_thread = unsafe { &*root.get().unwrap() };
-            script_thread.handle_page_headers_available(id, subpage, metadata)
+            script_thread.handle_page_headers_available(id, metadata)
         })
     }
 
@@ -877,8 +877,8 @@ impl ScriptThread {
 
     fn handle_msg_from_constellation(&self, msg: ConstellationControlMsg) {
         match msg {
-            ConstellationControlMsg::Navigate(parent_pipeline_id, subpage_id, load_data) =>
-                self.handle_navigate(parent_pipeline_id, Some(subpage_id), load_data),
+            ConstellationControlMsg::Navigate(parent_pipeline_id, pipeline_id, load_data) =>
+                self.handle_navigate(parent_pipeline_id, Some(pipeline_id), load_data),
             ConstellationControlMsg::SendEvent(id, event) =>
                 self.handle_event(id, event),
             ConstellationControlMsg::ResizeInactive(id, new_size) =>
@@ -894,21 +894,19 @@ impl ScriptThread {
             ConstellationControlMsg::NotifyVisibilityChange(parent_pipeline_id, pipeline_id, visible) =>
                 self.handle_visibility_change_complete_msg(parent_pipeline_id, pipeline_id, visible),
             ConstellationControlMsg::MozBrowserEvent(parent_pipeline_id,
-                                                     subpage_id,
+                                                     pipeline_id,
                                                      event) =>
                 self.handle_mozbrowser_event_msg(parent_pipeline_id,
-                                                 subpage_id,
+                                                 pipeline_id,
                                                  event),
-            ConstellationControlMsg::UpdateSubpageId(parent_pipeline_id,
-                                                     old_subpage_id,
-                                                     new_subpage_id,
-                                                     new_pipeline_id) =>
-                self.handle_update_subpage_id(parent_pipeline_id,
-                                              old_subpage_id,
-                                              new_subpage_id,
-                                              new_pipeline_id),
-            ConstellationControlMsg::FocusIFrame(parent_pipeline_id, subpage_id) =>
-                self.handle_focus_iframe_msg(parent_pipeline_id, subpage_id),
+            ConstellationControlMsg::UpdatePipelineId(parent_pipeline_id,
+                                                      old_pipeline_id,
+                                                      new_pipeline_id) =>
+                self.handle_update_pipeline_id(parent_pipeline_id,
+                                               old_pipeline_id,
+                                               new_pipeline_id),
+            ConstellationControlMsg::FocusIFrame(parent_pipeline_id, pipeline_id) =>
+                self.handle_focus_iframe_msg(parent_pipeline_id, pipeline_id),
             ConstellationControlMsg::WebDriverScriptCommand(pipeline_id, msg) =>
                 self.handle_webdriver_msg(pipeline_id, msg),
             ConstellationControlMsg::TickAllAnimations(pipeline_id) =>
@@ -1130,7 +1128,6 @@ impl ScriptThread {
         let NewLayoutInfo {
             parent_pipeline_id,
             new_pipeline_id,
-            subpage_id,
             frame_type,
             load_data,
             paint_chan,
@@ -1169,7 +1166,7 @@ impl ScriptThread {
                      .unwrap();
 
         // Kick off the fetch for the new resource.
-        let new_load = InProgressLoad::new(new_pipeline_id, Some((parent_pipeline_id, subpage_id, frame_type)),
+        let new_load = InProgressLoad::new(new_pipeline_id, Some((parent_pipeline_id, frame_type)),
                                            layout_chan, parent_window.window_size(),
                                            load_data.url.clone());
         self.start_page_load(new_load, load_data);
@@ -1257,7 +1254,7 @@ impl ScriptThread {
     fn handle_visibility_change_complete_msg(&self, parent_pipeline_id: PipelineId, id: PipelineId, visible: bool) {
         if let Some(root_context) = self.browsing_context.get() {
             if let Some(ref inner_context) = root_context.find(parent_pipeline_id) {
-                if let Some(iframe) = inner_context.active_document().find_iframe_by_pipeline(id) {
+                if let Some(iframe) = inner_context.active_document().find_iframe(id) {
                     iframe.change_visibility_status(visible);
                 }
             }
@@ -1323,12 +1320,12 @@ impl ScriptThread {
 
     fn handle_focus_iframe_msg(&self,
                                parent_pipeline_id: PipelineId,
-                               subpage_id: SubpageId) {
+                               pipeline_id: PipelineId) {
         let borrowed_context = self.root_browsing_context();
         let context = borrowed_context.find(parent_pipeline_id).unwrap();
 
         let doc = context.active_document();
-        let frame_element = doc.find_iframe(subpage_id);
+        let frame_element = doc.find_iframe(pipeline_id);
 
         if let Some(ref frame_element) = frame_element {
             doc.begin_focus_transaction();
@@ -1339,11 +1336,11 @@ impl ScriptThread {
 
     fn handle_framed_content_changed(&self,
                                      parent_pipeline_id: PipelineId,
-                                     subpage_id: SubpageId) {
+                                     pipeline_id: PipelineId) {
         let root_context = self.root_browsing_context();
         let context = root_context.find(parent_pipeline_id).unwrap();
         let doc = context.active_document();
-        let frame_element = doc.find_iframe(subpage_id);
+        let frame_element = doc.find_iframe(pipeline_id);
         if let Some(ref frame_element) = frame_element {
             frame_element.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
             let window = context.active_window();
@@ -1357,33 +1354,32 @@ impl ScriptThread {
     /// https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowserloadstart
     fn handle_mozbrowser_event_msg(&self,
                                    parent_pipeline_id: PipelineId,
-                                   subpage_id: Option<SubpageId>,
+                                   pipeline_id: Option<PipelineId>,
                                    event: MozBrowserEvent) {
         match self.root_browsing_context().find(parent_pipeline_id) {
             None => warn!("Mozbrowser event after pipeline {:?} closed.", parent_pipeline_id),
-            Some(context) => match subpage_id {
+            Some(context) => match pipeline_id {
                 None => context.active_window().dispatch_mozbrowser_event(event),
-                Some(subpage_id) => match context.active_document().find_iframe(subpage_id) {
-                    None => warn!("Mozbrowser event after iframe {:?}/{:?} closed.", parent_pipeline_id, subpage_id),
+                Some(pipeline_id) => match context.active_document().find_iframe(pipeline_id) {
+                    None => warn!("Mozbrowser event after iframe {:?}/{:?} closed.", parent_pipeline_id, pipeline_id),
                     Some(frame_element) => frame_element.dispatch_mozbrowser_event(event),
                 },
             },
         }
     }
 
-    fn handle_update_subpage_id(&self,
-                                parent_pipeline_id: PipelineId,
-                                old_subpage_id: SubpageId,
-                                new_subpage_id: SubpageId,
-                                new_pipeline_id: PipelineId) {
+    fn handle_update_pipeline_id(&self,
+                                 parent_pipeline_id: PipelineId,
+                                 old_pipeline_id: PipelineId,
+                                 new_pipeline_id: PipelineId) {
         let borrowed_context = self.root_browsing_context();
 
         let frame_element = borrowed_context.find(parent_pipeline_id).and_then(|context| {
             let doc = context.active_document();
-            doc.find_iframe(old_subpage_id)
+            doc.find_iframe(old_pipeline_id)
         });
 
-        frame_element.unwrap().update_subpage_id(new_subpage_id, new_pipeline_id);
+        frame_element.unwrap().update_pipeline_id(new_pipeline_id);
     }
 
     /// Window was resized, but this script was not active, so don't reflow yet
@@ -1412,11 +1408,9 @@ impl ScriptThread {
 
     /// We have received notification that the response associated with a load has completed.
     /// Kick off the document and frame tree creation process using the result.
-    fn handle_page_headers_available(&self, id: &PipelineId, subpage: Option<&SubpageId>,
+    fn handle_page_headers_available(&self, id: &PipelineId,
                                      metadata: Option<Metadata>) -> Option<ParserRoot> {
-        let idx = self.incomplete_loads.borrow().iter().position(|load| {
-            load.pipeline_id == *id && load.parent_info.as_ref().map(|info| &info.1) == subpage
-        });
+        let idx = self.incomplete_loads.borrow().iter().position(|load| { load.pipeline_id == *id });
         // The matching in progress load structure may not exist if
         // the pipeline exited before the page load completed.
         match idx {
@@ -1539,7 +1533,7 @@ impl ScriptThread {
             Some(browsing_context) => browsing_context.active_document(),
             None => return warn!("Message sent to closed pipeline {}.", parent_pipeline_id),
         };
-        if let Some(iframe) = document.find_iframe_by_pipeline(id) {
+        if let Some(iframe) = document.find_iframe(id) {
             iframe.iframe_load_event_steps(id);
         }
     }
@@ -1561,7 +1555,7 @@ impl ScriptThread {
         }
         debug!("ScriptThread: loading {} on pipeline {:?}", incomplete.url, incomplete.pipeline_id);
 
-        let frame_element = incomplete.parent_info.and_then(|(parent_id, subpage_id, _)| {
+        let frame_element = incomplete.parent_info.and_then(|(parent_id, _)| {
             // The root context may not exist yet, if the parent of this frame
             // exists in a different script thread.
             let root_context = self.browsing_context.get();
@@ -1576,7 +1570,7 @@ impl ScriptThread {
             root_context.and_then(|root_context| {
                 root_context.find(parent_id).and_then(|context| {
                     let doc = context.active_document();
-                    doc.find_iframe(subpage_id)
+                    doc.find_iframe(incomplete.pipeline_id)
                 })
             })
         });
@@ -1664,7 +1658,7 @@ impl ScriptThread {
             // We have a new root frame tree.
             self.browsing_context.set(Some(&new_context));
             (new_context, ContextToRemove::Root)
-        } else if let Some((parent, _, _)) = incomplete.parent_info {
+        } else if let Some((parent, _)) = incomplete.parent_info {
             // Create a new context tree entry. This will be a child context.
             let new_context = BrowsingContext::new(&window, frame_element, incomplete.pipeline_id);
 
@@ -2006,7 +2000,7 @@ impl ScriptThread {
     /// https://html.spec.whatwg.org/multipage/#navigating-across-documents
     /// The entry point for content to notify that a new load has been requested
     /// for the given pipeline (specifically the "navigate" algorithm).
-    fn handle_navigate(&self, parent_pipeline_id: PipelineId, subpage_id: Option<SubpageId>, load_data: LoadData) {
+    fn handle_navigate(&self, parent_pipeline_id: PipelineId, pipeline_id: Option<PipelineId>, load_data: LoadData) {
         // Step 7.
         {
             let nurl = &load_data.url;
@@ -2024,12 +2018,12 @@ impl ScriptThread {
             }
         }
 
-        match subpage_id {
-            Some(subpage_id) => {
+        match pipeline_id {
+            Some(pipeline_id) => {
                 let root_context = self.root_browsing_context();
                 let iframe = root_context.find(parent_pipeline_id).and_then(|context| {
                     let doc = context.active_document();
-                    doc.find_iframe(subpage_id)
+                    doc.find_iframe(pipeline_id)
                 });
                 if let Some(iframe) = iframe.r() {
                     iframe.navigate_or_reload_child_browsing_context(Some(load_data));
@@ -2076,9 +2070,8 @@ impl ScriptThread {
     /// argument until a notification is received that the fetch is complete.
     fn start_page_load(&self, incomplete: InProgressLoad, mut load_data: LoadData) {
         let id = incomplete.pipeline_id.clone();
-        let subpage = incomplete.parent_info.clone().map(|p| p.1);
 
-        let context = Arc::new(Mutex::new(ParserContext::new(id, subpage, load_data.url.clone())));
+        let context = Arc::new(Mutex::new(ParserContext::new(id, load_data.url.clone())));
         let (action_sender, action_receiver) = ipc::channel().unwrap();
         let listener = NetworkListener {
             context: context,