LatencyInfo trace_id_ no longer dependent on sequence_number.

cc/trees/latency_info_swap_promise_monitor.cc

Index: cc/trees/latency_info_swap_promise_monitor.cc
diff --git a/cc/trees/latency_info_swap_promise_monitor.cc b/cc/trees/latency_info_swap_promise_monitor.cc
index cb0af9ee9a286440c58d85b62332d96ffae723e2..c8e933dac6dc916a50ec6a14cdb197f1bcdb7789 100644
--- a/cc/trees/latency_info_swap_promise_monitor.cc
+++ b/cc/trees/latency_info_swap_promise_monitor.cc
@@ -90,12 +90,12 @@ void LatencyInfoSwapPromiseMonitor::OnForwardScrollUpdateToMainThreadOnImpl() {
     if (!new_sequence_number)
       return;
     ui::LatencyInfo new_latency;
-    new_latency.AddLatencyNumberWithTraceName(
-        ui::LATENCY_BEGIN_SCROLL_LISTENER_UPDATE_MAIN_COMPONENT, 0,
-        new_sequence_number, "ScrollUpdate");
     new_latency.CopyLatencyFrom(
         *latency_,
         ui::INPUT_EVENT_LATENCY_FORWARD_SCROLL_UPDATE_TO_MAIN_COMPONENT);

[brianderson, 2017/06/27 18:00:58]

The new order here seems more intuitive, but how did it work before?

[tdresser, 2017/06/27 18:33:11]

Both CopyLatencyFrom and AddLatencyNumberWithTraceName just add components. An
earlier version of this required this reorder, at this point it's just cosmetic.

+    new_latency.AddLatencyNumberWithTraceName(
+        ui::LATENCY_BEGIN_SCROLL_LISTENER_UPDATE_MAIN_COMPONENT, 0,
+        new_sequence_number, "ScrollUpdate");
     std::unique_ptr<SwapPromise> swap_promise(
         new LatencyInfoSwapPromise(new_latency));
     layer_tree_host_impl_->QueueSwapPromiseForMainThreadScrollUpdate(