CC Animation: Unify ElementId in Blink Compositor Worker.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index c4795d0996e1ac36e97a06ff3469c3bf75b1c775..ea028feff27961cd8d353b1dd7b1bad25e0f313f 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -33,6 +33,7 @@
 #include "cc/quads/shared_quad_state.h"
 #include "cc/resources/resource_provider.h"
 #include "cc/tiles/tile_priority.h"
+#include "cc/trees/element_id.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "ui/gfx/geometry/point3_f.h"
@@ -244,8 +245,8 @@ class CC_EXPORT LayerImpl {
   bool HasPotentiallyRunningOpacityAnimation() const;
   bool OpacityIsAnimatingOnImplOnly() const;
 
-  void SetElementId(uint64_t element_id);
-  uint64_t element_id() const { return element_id_; }
+  void SetElementId(ElementId element_id);
+  ElementId element_id() const { return element_id_; }
 
   void SetMutableProperties(uint32_t properties);
   uint32_t mutable_properties() const { return mutable_properties_; }
@@ -635,7 +636,7 @@ class CC_EXPORT LayerImpl {
   DrawMode current_draw_mode_;
 
  private:
-  uint64_t element_id_;
+  ElementId element_id_;
   uint32_t mutable_properties_;
   // Rect indicating what was repainted/updated during update.
   // Note that plugin layers bypass this and leave it empty.