Change cc::ElementId to be a uint64_t

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 5fb4b6d11253ec983dada5606dcd9f5d31910467..22fe99c82b03f97ff6928f4ea8a1ad7ed4a6f2f8 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3437,7 +3437,7 @@ void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point) {
   // TODO(sahel): get rid of this extera checking when
   // FindScrollNodeForDeviceViewportPoint finds the proper node for scrolling on
   // the main thread when the mouse is over a scrollbar as well.
-  ElementId scroll_element_id;
+  ElementId scroll_element_id = 0;
   if (layer_impl && layer_impl->ToScrollbarLayer())
     scroll_element_id = layer_impl->ToScrollbarLayer()->scroll_element_id();
   if (!scroll_element_id) {
@@ -3546,8 +3546,8 @@ static void CollectScrollDeltas(ScrollAndScaleSet* scroll_info,
 static void CollectScrollbarUpdates(
     ScrollAndScaleSet* scroll_info,
     std::unordered_map<ElementId,
-                       std::unique_ptr<ScrollbarAnimationController>,
-                       ElementIdHash>* controllers) {
+                       std::unique_ptr<ScrollbarAnimationController>>*
+        controllers) {
   scroll_info->scrollbars.reserve(controllers->size());
   for (auto& pair : *controllers) {
     scroll_info->scrollbars.push_back(LayerTreeHostCommon::ScrollbarsUpdateInfo(