CC Animation: Unify ElementId in Blink Compositor Worker.

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index 97e83c339b461fbb9523b05e55835b552d39877a..63e3c1be91b9e5cd2c29ed0f470f169b1a40a3a7 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -26,6 +26,7 @@
 #include "cc/layers/layer_position_constraint.h"
 #include "cc/layers/paint_properties.h"
 #include "cc/output/filter_operations.h"
+#include "cc/trees/element_id.h"
 #include "cc/trees/property_tree.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
@@ -492,8 +493,8 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
 
   int num_copy_requests_in_target_subtree();
 
-  void SetElementId(uint64_t id);
-  uint64_t element_id() const { return element_id_; }
+  void SetElementId(ElementId id);
+  ElementId element_id() const { return element_id_; }
 
   void SetMutableProperties(uint32_t properties);
   uint32_t mutable_properties() const { return mutable_properties_; }
@@ -621,7 +622,7 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
   int clip_tree_index_;
   int scroll_tree_index_;
   int property_tree_sequence_number_;
-  uint64_t element_id_;
+  ElementId element_id_;
   uint32_t mutable_properties_;
   gfx::Vector2dF offset_to_transform_parent_;
   uint32_t main_thread_scrolling_reasons_;