Trace main thread commit in flow events.

cc/output/latency_info_swap_promise.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/latency_info_swap_promise.h"
 
 #include "base/logging.h"
+#include "base/trace_event/trace_event.h"
 
 namespace {
 ui::LatencyComponentType DidNotSwapReasonToLatencyComponentType(
     cc::SwapPromise::DidNotSwapReason reason) {
   switch (reason) {
     case cc::SwapPromise::ACTIVATION_FAILS:
     case cc::SwapPromise::SWAP_FAILS:
       return ui::INPUT_EVENT_LATENCY_TERMINATED_SWAP_FAILED_COMPONENT;
     case cc::SwapPromise::COMMIT_FAILS:
       return ui::INPUT_EVENT_LATENCY_TERMINATED_COMMIT_FAILED_COMPONENT;
@@ skipping 24 matching lines @@
                             0);
   // TODO(miletus): Turn this back on once per-event LatencyInfo tracking
   // is enabled in GPU side.
   // DCHECK(latency_.terminated);
 }
 
 int64 LatencyInfoSwapPromise::TraceId() const {
   return latency_.trace_id;
 }
 
+// Trace the original LatencyInfo of a LatencyInfoSwapPromise
+void LatencyInfoSwapPromise::OnCommit() {
+  TRACE_EVENT_FLOW_STEP0("input,benchmark", "LatencyInfo.Flow",
+                         TRACE_ID_DONT_MANGLE(TraceId()),
+                         "HanldeInputEventMainCommit");
+}
+
 }  // namespace cc