[cc] Remove BeginFrameAck from BFS::DidFinishFrame and update tests.

cc/test/fake_external_begin_frame_source.h

 // 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.
 
 #ifndef CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 #define CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 
 #include <set>
 
 #include "base/cancelable_callback.h"
@@ skipping 21 matching lines @@
   explicit FakeExternalBeginFrameSource(double refresh_rate,
                                         bool tick_automatically);
   ~FakeExternalBeginFrameSource() override;
 
   void SetClient(Client* client) { client_ = client; }
   void SetPaused(bool paused);
 
   // BeginFrameSource implementation.
   void AddObserver(BeginFrameObserver* obs) override;
   void RemoveObserver(BeginFrameObserver* obs) override;
-  void DidFinishFrame(BeginFrameObserver* obs,
-                      const BeginFrameAck& ack) override;
+  void DidFinishFrame(BeginFrameObserver* obs) override;
   bool IsThrottled() const override;
 
   BeginFrameArgs CreateBeginFrameArgs(
       BeginFrameArgs::CreationLocation location);
   BeginFrameArgs CreateBeginFrameArgs(BeginFrameArgs::CreationLocation location,
                                       base::SimpleTestTickClock* now_src);
   uint64_t next_begin_frame_number() const { return next_begin_frame_number_; }
 
   void TestOnBeginFrame(const BeginFrameArgs& args);
 
   size_t num_observers() const { return observers_.size(); }
 
-  const BeginFrameAck& LastAckForObserver(BeginFrameObserver* obs) {
-    return last_acks_[obs];
-  }
-
  private:
   void PostTestOnBeginFrame();
 
   const bool tick_automatically_;
   const double milliseconds_per_frame_;
   Client* client_ = nullptr;
   bool paused_ = false;
   BeginFrameArgs current_args_;
   uint64_t next_begin_frame_number_ = BeginFrameArgs::kStartingFrameNumber;
   std::set<BeginFrameObserver*> observers_;
   base::CancelableCallback<void(const BeginFrameArgs&)> begin_frame_task_;
-  std::unordered_map<BeginFrameObserver*, BeginFrameAck> last_acks_;
   base::WeakPtrFactory<FakeExternalBeginFrameSource> weak_ptr_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_