Use element id's for animations

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 141b610f6c3d12922976278789658f01fa4615da..a127f35d44dcffdaaf6fb2845c07674d637c36da 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -18,6 +18,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/values.h"
+#include "cc/animation/element_id.h"
 #include "cc/animation/target_property.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/region.h"
@@ -235,8 +236,8 @@ class CC_EXPORT LayerImpl {
   bool OpacityIsAnimating() const;
   bool HasPotentiallyRunningOpacityAnimation() 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_; }
@@ -618,7 +619,7 @@ 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.