LatencyInfo trace_id_ no longer dependent on sequence_number.

cc/ipc/struct_traits_unittest.cc

Index: cc/ipc/struct_traits_unittest.cc
diff --git a/cc/ipc/struct_traits_unittest.cc b/cc/ipc/struct_traits_unittest.cc
index a5190b561b633f8f9110c0f2aefc15906fbba04e..dc5d9cbe56c97eecdeab77266cb1e704533e3ca1 100644
--- a/cc/ipc/struct_traits_unittest.cc
+++ b/cc/ipc/struct_traits_unittest.cc
@@ -362,6 +362,7 @@ TEST_F(StructTraitsTest, CompositorFrameMetadata) {
   selection.end.set_visible(false);
   selection.end.set_type(gfx::SelectionBound::RIGHT);
   ui::LatencyInfo latency_info;
+  latency_info.set_trace_id(5);
   latency_info.AddLatencyNumber(
       ui::LATENCY_BEGIN_SCROLL_LISTENER_UPDATE_MAIN_COMPONENT, 1337, 7331);
   std::vector<ui::LatencyInfo> latency_infos = {latency_info};