Use element id's for animations

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index c56ff2998d920c18605c3655be549ae6450d3cf4..2ab8108aa403ba382d8801dcbaa480ce41853759 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -17,6 +17,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
+#include "cc/animation/element_id.h"
 #include "cc/animation/target_property.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/region.h"
@@ -488,8 +489,8 @@ 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_; }
@@ -625,7 +626,7 @@ 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_;