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..b28d5df96371cbf4dc730c602453f5410375da98 100644
--- a/cc/test/animation_timelines_test_common.cc
+++ b/cc/test/animation_timelines_test_common.cc
@@ -351,11 +351,12 @@ AnimationTimelinesTest::AnimationTimelinesTest()
       host_impl_(nullptr),
       timeline_id_(AnimationIdProvider::NextTimelineId()),
       player_id_(AnimationIdProvider::NextPlayerId()),
+      element_id_(kInvalidElementId),
       next_test_layer_id_(0) {
   host_ = client_.host();
   host_impl_ = client_impl_.host();
 
-  element_id_ = ElementId(NextTestLayerId(), 0);
+  element_id_ = NextTestLayerId();
 }
 
 AnimationTimelinesTest::~AnimationTimelinesTest() {