CC Animations: Make ui::LayerAnimator a LayerAnimationEventObserver (instead of ui::Layer)

ui/compositor/layer_animator.cc

Index: ui/compositor/layer_animator.cc
diff --git a/ui/compositor/layer_animator.cc b/ui/compositor/layer_animator.cc
index 4d063ecd6e94d2afd591b0569ed2bdf6aa90a509..b4afd2e0dfc30d31bbfaf65ac10880ba0deba818 100644
--- a/ui/compositor/layer_animator.cc
+++ b/ui/compositor/layer_animator.cc
@@ -115,6 +115,7 @@ void LayerAnimator::SetDelegate(LayerAnimationDelegate* delegate) {
     if (collection)
       collection->StopAnimator(this);
   }
+  SwitchToLayer(delegate ? delegate->GetCcLayer() : nullptr);
   delegate_ = delegate;
   if (delegate_ && is_started_) {
     LayerAnimatorCollection* collection = GetLayerAnimatorCollection();
@@ -123,6 +124,15 @@ void LayerAnimator::SetDelegate(LayerAnimationDelegate* delegate) {
   }
 }
 
+void LayerAnimator::SwitchToLayer(scoped_refptr<cc::Layer> new_layer) {
+  if (delegate_) {
+    DCHECK(delegate_->GetCcLayer());
+    delegate_->GetCcLayer()->RemoveLayerAnimationEventObserver(this);
+  }
+  if (new_layer)
+    new_layer->AddLayerAnimationEventObserver(this);
+}
+
 void LayerAnimator::StartAnimation(LayerAnimationSequence* animation) {
   scoped_refptr<LayerAnimator> retain(this);
   OnScheduled(animation);
@@ -850,6 +860,10 @@ LayerAnimatorCollection* LayerAnimator::GetLayerAnimatorCollection() {
   return delegate_ ? delegate_->GetLayerAnimatorCollection() : NULL;
 }
 
+void LayerAnimator::OnAnimationStarted(const cc::AnimationEvent& event) {
+  OnThreadedAnimationStarted(event);
+}
+
 LayerAnimator::RunningAnimation::RunningAnimation(
     const base::WeakPtr<LayerAnimationSequence>& sequence)
     : sequence_(sequence) {