Remove CompositorObserver::OnCompositingEnded()

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 81a934550879bc91ea2e3d17bc273a65b206dbe4..cdb78a55720cac8def13b32e29115b133df6b465 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -529,14 +529,11 @@ void Compositor::DidCommit() {
     observer.OnCompositingDidCommit(this);
 }
 
-void Compositor::DidReceiveCompositorFrameAck() {
-  ++committed_frame_number_;
-  for (auto& observer : observer_list_)
-    observer.OnCompositingEnded(this);
-}
+void Compositor::DidReceiveCompositorFrameAck() {}
 
 void Compositor::DidSubmitCompositorFrame() {
   base::TimeTicks start_time = base::TimeTicks::Now();
+  ++committed_frame_number_;

[danakj, 2017/03/28 16:04:54]

This would change the result of Layer::GetFrameNumber. I started trying to track
down all callers of that to see if any would happen after
DidSubmitCompositorFrame and before DidReceiveCompositorFrameAck, but there's
many callers, so can you do that to convince yourself and me that it's okay? In
the end its about animation ticking afaict. If you're stuck ajuma can help.

[Fady Samuel, 2017/03/28 17:35:05]

As I said offline, we can undo this change and land the rest of the patch then
figure out the right way to measure animation jank separately.

[Alex Z., 2017/03/28 18:08:27]

This change has been reverted in the latest patch.

   for (auto& observer : observer_list_)
     observer.OnCompositingStarted(this, start_time);
 }