Implement a new flow event API that allows binding flow events and regular events.

cc/scheduler/begin_frame_tracker.cc

 // Copyright 2014 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/scheduler/begin_frame_tracker.h"
 
 namespace cc {
 
 BeginFrameTracker::BeginFrameTracker(const tracked_objects::Location& location)
     : location_(location),
       location_string_(location.ToString()),
       current_updated_at_(),
       current_args_(),
       current_finished_at_(base::TraceTicks::FromInternalValue(-1)) {
 }
 
 BeginFrameTracker::~BeginFrameTracker() {
 }
 
 void BeginFrameTracker::Start(BeginFrameArgs new_args) {
   // Trace the frame time being passed between BeginFrameTrackers.
+  TRACE_EVENT_WITH_FLOW0("toplevel", "BeginFrameTracker::Start",
+                         new_args.frame_time.ToInternalValue(),
+                         TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT);
   TRACE_EVENT_FLOW_STEP0(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.frames"), "BeginFrameArgs",
       new_args.frame_time.ToInternalValue(), location_string_);
 
   // Trace this specific begin frame tracker Start/Finish times.
   TRACE_EVENT_ASYNC_BEGIN2(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.frames"),
       location_string_.c_str(), new_args.frame_time.ToInternalValue(),
       "new args", new_args.AsValue(), "current args", current_args_.AsValue());
 
@@ skipping 82 matching lines @@
 
 const BeginFrameArgs& BeginFrameTracker::DangerousMethodCurrentOrLast() const {
   if (!HasFinished()) {
     return Current();
   } else {
     return Last();
   }
 }
 
 }  // namespace cc