[VSync Queue] Add tracing for event queuing time and coalesced count

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 9e93d478e93aedff7a48160faadf69ac27caed55..c8e977a7d321ab0bda827e2e51a5ef3fec770352 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -295,6 +295,7 @@ void InputHandlerProxy::HandleInputEventWithLatencyInfo(
     const LatencyInfo& latency_info,
     const EventDispositionCallback& callback) {
   DCHECK(input_handler_);
+  TRACE_EVENT0("input", "InputHandlerProxy::HandleInputEventWithLatencyInfo");
 
   if (uma_latency_reporting_enabled_)
     ReportInputEventLatencyUma(*event, latency_info);
@@ -335,11 +336,17 @@ void InputHandlerProxy::HandleInputEventWithLatencyInfo(
 void InputHandlerProxy::DispatchSingleInputEvent(
     std::unique_ptr<EventWithCallback> event_with_callback,
     const base::TimeTicks now) {
+  TRACE_EVENT0("input", "InputHandlerProxy::DispatchSingleInputEvent");
   if (compositor_event_queue_ &&
       IsGestureScollOrPinch(event_with_callback->event().type())) {
     // Report the coalesced count only for continuous events to avoid the noise
     // from non-continuous events.
     if (IsContinuousGestureEvent(event_with_callback->event().type())) {
+      TRACE_EVENT_INSTANT2(
+          "input", "InputHandlerProxy::CoalescedContinusGestureEvent",

[tdresser, 2017/02/14 16:31:54]

Continuous

+          TRACE_EVENT_SCOPE_THREAD, "type", event_with_callback->event().type(),
+          "coalesced_count", event_with_callback->coalesced_count());
+
       UMA_HISTOGRAM_CUSTOM_COUNTS(
           "Event.CompositorThreadEventQueue.Continuous.HeadQueueingTime",
           (now - event_with_callback->creation_timestamp()).InMicroseconds(), 1,