Ensures that iframe navigation updates the parent iframe element subpage id.

This fixes the case of clicking a link in an iframe, going back, then clicking the link again.

components/compositing/constellation.rs

@@ -608,6 +608,16 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         // Set paint permissions correctly for the compositor layers.
         self.revoke_paint_permission(prev_pipeline_id);
         self.send_frame_tree_and_grant_paint_permission();
+
+        // Update the owning iframe to point to the new subpage id.
+        // This makes things like contentDocument work correctly.
+        if let Some((parent_pipeline_id, subpage_id)) = pipeline_info {
+            let ScriptControlChan(ref script_chan) = self.pipeline(parent_pipeline_id).script_chan;
+            let (_, new_subpage_id) = self.pipeline(next_pipeline_id).parent_info.unwrap();
+            script_chan.send(ConstellationControlMsg::UpdateSubpageId(parent_pipeline_id,
+                                                                      subpage_id,
+                                                                      new_subpage_id)).unwrap();
+        }
     }
 
     fn handle_key_msg(&self, key: Key, state: KeyState, mods: KeyModifiers) {

components/script/dom/htmliframeelement.rs

@@ -73,6 +73,7 @@ pub trait HTMLIFrameElementHelpers {
     fn generate_new_subpage_id(self) -> (SubpageId, Option<SubpageId>);
     fn navigate_child_browsing_context(self, url: Url);
     fn dispatch_mozbrowser_event(self, event_name: String, event_detail: Option<String>);
+    fn update_subpage_id(self, new_subpage_id: SubpageId);
 }
 
 impl<'a> HTMLIFrameElementHelpers for JSRef<'a, HTMLIFrameElement> {
@@ -156,6 +157,10 @@ impl<'a> HTMLIFrameElementHelpers for JSRef<'a, HTMLIFrameElement> {
             event.fire(target);
         }
     }
+
+    fn update_subpage_id(self, new_subpage_id: SubpageId) {
+        self.subpage_id.set(Some(new_subpage_id));
+    }
 }
 
 impl HTMLIFrameElement {

components/script/script_task.rs

@@ -652,6 +652,10 @@ impl ScriptTask {
                                                  subpage_id,
                                                  event_name,
                                                  event_detail),
+            ConstellationControlMsg::UpdateSubpageId(containing_pipeline_id,
+                                                     old_subpage_id,
+                                                     new_subpage_id) =>
+                self.handle_update_subpage_id(containing_pipeline_id, old_subpage_id, new_subpage_id),
         }
     }
 
@@ -817,6 +821,25 @@ impl ScriptTask {
         }
     }
 
+    fn handle_update_subpage_id(&self,
+                                containing_pipeline_id: PipelineId,
+                                old_subpage_id: SubpageId,
+                                new_subpage_id: SubpageId) {
+        let borrowed_page = self.root_page();
+
+        let frame_element = borrowed_page.find(containing_pipeline_id).and_then(|page| {
+            let doc = page.document().root();
+            let doc: JSRef<Node> = NodeCast::from_ref(doc.r());
+
+            doc.traverse_preorder()
+               .filter_map(HTMLIFrameElementCast::to_ref)
+               .find(|node| node.subpage_id() == Some(old_subpage_id))
+               .map(Temporary::from_rooted)
+        }).root();
+
+        frame_element.unwrap().r().update_subpage_id(new_subpage_id);
+    }
+
     /// Handles a notification that reflow completed.
     fn handle_reflow_complete_msg(&self, pipeline_id: PipelineId, reflow_id: uint) {
         debug!("Script: Reflow {:?} complete for {:?}", reflow_id, pipeline_id);

components/script_traits/lib.rs

@@ -74,6 +74,8 @@ pub enum ConstellationControlMsg {
     Navigate(PipelineId, SubpageId, LoadData),
     /// Requests the script task forward a mozbrowser event to an iframe it owns
     MozBrowserEvent(PipelineId, SubpageId, String, Option<String>),
+    /// Updates the current subpage id of a given iframe
+    UpdateSubpageId(PipelineId, SubpageId, SubpageId),
 }
 
 unsafe impl Send for ConstellationControlMsg {