CC Animation: Use ElementId to attach CC animation players.

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 b3474964bcfeb46668c57344a8926907631d27b6..dd2ea4afaf7e5f52005b91bfe00aa0ca03ec3e1b 100644
--- a/ui/compositor/layer_animator.cc
+++ b/ui/compositor/layer_animator.cc
@@ -139,9 +139,12 @@ void LayerAnimator::SwitchToLayer(scoped_refptr<cc::Layer> new_layer) {
   element_animations_state_ = nullptr;
 
   if (delegate_)
-    DetachLayerFromAnimationPlayer();
-  if (new_layer)
-    AttachLayerToAnimationPlayer(new_layer->id());
+    DetachElementFromAnimationPlayer();
+  if (new_layer) {
+    if (!new_layer->element_id())
+      new_layer->SetElementId(Layer::NextElementId());
+    AttachElementToAnimationPlayer(new_layer->element_id());
+  }
 }
 
 void LayerAnimator::SetCompositor(Compositor* compositor) {
@@ -157,14 +160,14 @@ void LayerAnimator::SetCompositor(Compositor* compositor) {
   // AnimationHost::GetElementAnimationsForLayerId.
   if (element_animations_state_) {
     DCHECK_EQ(element_animations_state_->element_id(),
-              delegate_->GetCcLayer()->id());
+              delegate_->GetCcLayer()->element_id());
     timeline->animation_host()->RegisterElementAnimations(
         element_animations_state_.get());
   }
 
   timeline->AttachPlayer(animation_player_);
 
-  AttachLayerToAnimationPlayer(delegate_->GetCcLayer()->id());
+  AttachElementToAnimationPlayer(delegate_->GetCcLayer()->element_id());
 
   // Release ElementAnimations state.
   element_animations_state_ = nullptr;
@@ -176,30 +179,33 @@ void LayerAnimator::ResetCompositor(Compositor* compositor) {
   cc::AnimationTimeline* timeline = compositor->GetAnimationTimeline();
   DCHECK(timeline);
 
-  const int layer_id = animation_player_->element_id();
+  const cc::ElementId element_id = animation_player_->element_id();
 
   // Store a reference to ElementAnimations (if any)
   // so it may be picked up in LayerAnimator::SetCompositor.
-  if (layer_id) {
+  if (element_id) {
     element_animations_state_ =
-        timeline->animation_host()->GetElementAnimationsForElementId(layer_id);
+        timeline->animation_host()->GetElementAnimationsForElementId(
+            element_id);
   }
 
-  DetachLayerFromAnimationPlayer();
+  DetachElementFromAnimationPlayer();
 
   timeline->DetachPlayer(animation_player_);
 }
 
-void LayerAnimator::AttachLayerToAnimationPlayer(int layer_id) {
+void LayerAnimator::AttachElementToAnimationPlayer(cc::ElementId element_id) {
+  DCHECK(element_id);
+
   if (!animation_player_->element_id())
-    animation_player_->AttachElement(layer_id);
+    animation_player_->AttachElement(element_id);
   else
-    DCHECK_EQ(animation_player_->element_id(), layer_id);
+    DCHECK_EQ(animation_player_->element_id(), element_id);
 
   animation_player_->set_animation_delegate(this);
 }
 
-void LayerAnimator::DetachLayerFromAnimationPlayer() {
+void LayerAnimator::DetachElementFromAnimationPlayer() {
   animation_player_->set_animation_delegate(nullptr);
 
   if (animation_player_->element_id())