Change cc::ElementId to be a uint64_t

cc/test/animation_timelines_test_common.cc

Index: cc/test/animation_timelines_test_common.cc
diff --git a/cc/test/animation_timelines_test_common.cc b/cc/test/animation_timelines_test_common.cc
index dd039a47a66388a93c81d0db6d79b60f8eac49d5..6fe7786cddb6203553e48299636da1a8678b9750 100644
--- a/cc/test/animation_timelines_test_common.cc
+++ b/cc/test/animation_timelines_test_common.cc
@@ -79,8 +79,8 @@ void TestHostClient::ClearMutatedProperties() {
 bool TestHostClient::IsElementInList(ElementId element_id,
                                      ElementListType list_type) const {
   return list_type == ElementListType::ACTIVE
-             ? layers_in_active_tree_.count(element_id)
-             : layers_in_pending_tree_.count(element_id);
+             ? layers_in_active_tree_.count(element_id.id)
+             : layers_in_pending_tree_.count(element_id.id);
 }
 
 void TestHostClient::SetMutatorsNeedCommit() {
@@ -160,8 +160,8 @@ void TestHostClient::RegisterElement(ElementId element_id,
   ElementIdToTestLayer& layers_in_tree = list_type == ElementListType::ACTIVE
                                              ? layers_in_active_tree_
                                              : layers_in_pending_tree_;
-  DCHECK(layers_in_tree.find(element_id) == layers_in_tree.end());
-  layers_in_tree[element_id] = TestLayer::Create();
+  DCHECK(layers_in_tree.find(element_id.id) == layers_in_tree.end());
+  layers_in_tree[element_id.id] = TestLayer::Create();
 
   DCHECK(host_);
   host_->RegisterElement(element_id, list_type);
@@ -175,7 +175,7 @@ void TestHostClient::UnregisterElement(ElementId element_id,
   ElementIdToTestLayer& layers_in_tree = list_type == ElementListType::ACTIVE
                                              ? layers_in_active_tree_
                                              : layers_in_pending_tree_;
-  auto kv = layers_in_tree.find(element_id);
+  auto kv = layers_in_tree.find(element_id.id);
   DCHECK(kv != layers_in_tree.end());
   layers_in_tree.erase(kv);
 }
@@ -299,7 +299,7 @@ TestLayer* TestHostClient::FindTestLayer(ElementId element_id,
   const ElementIdToTestLayer& layers_in_tree =
       list_type == ElementListType::ACTIVE ? layers_in_active_tree_
                                            : layers_in_pending_tree_;
-  auto kv = layers_in_tree.find(element_id);
+  auto kv = layers_in_tree.find(element_id.id);
   if (kv == layers_in_tree.end())
     return nullptr;
 
@@ -355,7 +355,7 @@ AnimationTimelinesTest::AnimationTimelinesTest()
   host_ = client_.host();
   host_impl_ = client_impl_.host();
 
-  element_id_ = ElementId(NextTestLayerId(), 0);
+  element_id_.id = NextTestLayerId();
 }
 
 AnimationTimelinesTest::~AnimationTimelinesTest() {