Restructure compositor layers to work with iframes

When a frame is selected via set_ids, a tree of root compositor
layers is also created, matching the tree of pipelines in the frame.
This decouples the chronological ordering dependency for parent frames
and child iframes sending CreateOrUpdateRootLayer &
CreateOrUpdateDescendentLayer messages.

Change the Compositor ready and render states to per pipeline.
This ensures the compositor doesn't composite for an epoch until
every *pipeline* in the epoch is finished rendering.

For iframes it fixes a bug where the compositor didnt wait on the
child pipeline ready state before compositing the window.

Gotchas:
* layout task or script task failure on exit ("task '' failed at sending
  on a closed channel"), this happens if the child iframe shares the
  same script task as the parent and can be avoided by adding the
  sandbox attribute to the iframe.

Other changes:
* Inline set_clipping_rect in compositor.rs
* Commented out ref test simple_iframe.html fails on os x

1 files changed, 2 insertions, 2 deletions

diff --git a/src/components/script/script_task.rs b/src/components/script/script_task.rs
index e173a37f762..51a4c5f3e51 100644
--- a/src/components/script/script_task.rs
+++ b/src/components/script/script_task.rs
@@ -452,7 +452,7 @@ impl ScriptTask {
             let mut layout_join_port = page.layout_join_port.deref().borrow_mut();
             *layout_join_port = None;
         }
-        self.compositor.set_ready_state(FinishedLoading);
+        self.compositor.set_ready_state(pipeline_id, FinishedLoading);
     }
 
     /// Handles a navigate forward or backward message.
@@ -549,7 +549,7 @@ impl ScriptTask {
         let document = Document::new(&*window, Some(url.clone()), HTMLDocument, None).root();
         window.deref().init_browser_context(&*document);
 
-        self.compositor.set_ready_state(Loading);
+        self.compositor.set_ready_state(pipeline_id, Loading);
         // Parse HTML.
         //
         // Note: We can parse the next document in parallel with any previous documents.