[cc] Add and use BeginFrameAck for DidFinishFrame.

cc/scheduler/begin_frame_source.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_source.h"
 
 #include <stddef.h>
 
 #include "base/atomic_sequence_num.h"
 #include "base/auto_reset.h"
@@ skipping 82 matching lines @@
 void BackToBackBeginFrameSource::RemoveObserver(BeginFrameObserver* obs) {
   DCHECK(obs);
   DCHECK(observers_.find(obs) != observers_.end());
   observers_.erase(obs);
   pending_begin_frame_observers_.erase(obs);
   if (pending_begin_frame_observers_.empty())
     time_source_->SetActive(false);
 }
 
 void BackToBackBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs,
-                                                size_t remaining_frames) {
-  if (remaining_frames == 0 && observers_.find(obs) != observers_.end()) {
+                                                const BeginFrameAck& ack) {
+  if (ack.remaining_frames == 0 && observers_.find(obs) != observers_.end()) {
     pending_begin_frame_observers_.insert(obs);
     time_source_->SetActive(true);
   }
 }
 
 bool BackToBackBeginFrameSource::IsThrottled() const {
   return false;
 }
 
 void BackToBackBeginFrameSource::OnTimerTick() {
@@ skipping 176 matching lines @@
 
 void ExternalBeginFrameSource::OnBeginFrame(const BeginFrameArgs& args) {
   missed_begin_frame_args_ = args;
   missed_begin_frame_args_.type = BeginFrameArgs::MISSED;
   std::unordered_set<BeginFrameObserver*> observers(observers_);
   for (auto* obs : observers)
     obs->OnBeginFrame(args);
 }
 
 }  // namespace cc