Change cc::ElementId to be a uint64_t

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 9546d4c399026fc58a1816f2fc18a5833e1e8167..60977192605c8845c28a8cb09e381015695cfb85 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -826,9 +826,7 @@ class CC_EXPORT LayerTreeHostImpl
 
   // Map from scroll element ID to scrollbar animation controller.
   // There is one animation controller per pair of overlay scrollbars.
-  std::unordered_map<ElementId,
-                     std::unique_ptr<ScrollbarAnimationController>,
-                     ElementIdHash>
+  std::unordered_map<ElementId, std::unique_ptr<ScrollbarAnimationController>>
       scrollbar_animation_controllers_;
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;