CC Animation: Use ElementId to attach CC animation players.

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index c671e31b83b5776ca25afe362111794f77d0e9fe..b928ff2bd7e1759b97dbc5418f4280a902c50abf 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -168,9 +168,11 @@ class CC_EXPORT LayerTreeImpl {
     LayerImpl* scroll = nullptr;
   };
 
+  void RegisterLayerForElementId(LayerImpl* layer);
+  void UnregisterLayerForElementId(LayerImpl* layer);
   void AddToElementMap(LayerImpl* layer);
   void RemoveFromElementMap(LayerImpl* layer);
-  ElementLayers GetMutableLayers(uint64_t element_id);
+  ElementLayers GetMutableLayers(ElementId element_id);
   int source_frame_number() const { return source_frame_number_; }
   void set_source_frame_number(int frame_number) {
     source_frame_number_ = frame_number;
@@ -304,6 +306,9 @@ class CC_EXPORT LayerTreeImpl {
   gfx::Rect RootScrollLayerDeviceViewportBounds() const;
 
   LayerImpl* LayerById(int id) const;
+  LayerImpl* LayerForElementId(ElementId element_id) const;
+  LayerImpl* ScrollLayerForElementId(ElementId element_id) const;
+  bool HasAnyLayerForElementId(ElementId element_id) const;
 
   void AddLayerShouldPushProperties(LayerImpl* layer);
   void RemoveLayerShouldPushProperties(LayerImpl* layer);
@@ -529,11 +534,15 @@ class CC_EXPORT LayerTreeImpl {
 
   std::unique_ptr<OwnedLayerImplList> layers_;
   LayerImplMap layer_id_map_;
+
+  using ElementIdToLayerMap = std::unordered_map<ElementId, ElementLayers>;
+  ElementIdToLayerMap element_id_to_layer_map_;
+  // TODO(loyso): Unify it with element_id_to_layer_map_.
+  std::unordered_map<ElementId, ElementLayers> element_layers_map_;
+
   // Set of layers that need to push properties.
   std::unordered_set<LayerImpl*> layers_that_should_push_properties_;
 
-  std::unordered_map<uint64_t, ElementLayers> element_layers_map_;
-
   // Maps from clip layer ids to scroll layer ids.  Note that this only includes
   // the subset of clip layers that act as scrolling containers.  (This is
   // derived from LayerImpl::scroll_clip_layer_ and exists to avoid O(n) walks.)