Change cc::ElementId to be a uint64_t

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 8080c57afb3446bd07f2ac00ff77b4758ea965c5..78dd4cc6f552e54575a551529b20827f0e9a3595 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -380,7 +380,7 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
 
   // To maintain the current scrolling node we need to use element ids which
   // are stable across the property tree update in SetPropertyTrees.
-  ElementId scrolling_element_id;
+  ElementId scrolling_element_id = 0;
   if (ScrollNode* scrolling_node = target_tree->CurrentlyScrollingNode())
     scrolling_element_id = scrolling_node->element_id;
 
@@ -536,8 +536,8 @@ void LayerTreeImpl::AddToElementMap(LayerImpl* layer) {
     return;
 
   TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
-               "LayerTreeImpl::AddToElementMap", "element",
-               element_id.AsValue().release(), "layer_id", layer->id());
+               "LayerTreeImpl::AddToElementMap", "element", element_id,
+               "layer_id", layer->id());
 
 #if DCHECK_IS_ON()
   LayerImpl* existing_layer = LayerByElementId(element_id);
@@ -564,8 +564,7 @@ void LayerTreeImpl::RemoveFromElementMap(LayerImpl* layer) {
 
   TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
                "LayerTreeImpl::RemoveFromElementMap", "element",
-               layer->element_id().AsValue().release(), "layer_id",
-               layer->id());
+               layer->element_id(), "layer_id", layer->id());
 
   layer_tree_host_impl_->mutator_host()->UnregisterElement(
       layer->element_id(),
@@ -985,7 +984,7 @@ void LayerTreeImpl::ClearViewportLayers() {
 
 // For unit tests, we use the layer's id as its element id.
 static void SetElementIdForTesting(LayerImpl* layer) {
-  layer->SetElementId(LayerIdToElementIdForTesting(layer->id()));
+  layer->SetElementId(layer->id());
 }
 
 void LayerTreeImpl::SetElementIdsForTesting() {