Update AudioRenderer API to fire changes in BufferingState.

media/base/pipeline.h

 // Copyright (c) 2012 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 MEDIA_BASE_PIPELINE_H_
 #define MEDIA_BASE_PIPELINE_H_
 
 #include <string>
 
 #include "base/gtest_prod_util.h"
@@ skipping 291 matching lines @@
   // TODO(scherkus): Prerolling should be separate from seeking so we can report
   // finer grained ready states (HAVE_CURRENT_DATA vs. HAVE_FUTURE_DATA)
   // indepentent from seeking.
   void DoSeek(base::TimeDelta seek_timestamp, const PipelineStatusCB& done_cb);
 
   // Initiates an asynchronous pause-flush-stop call sequence executing
   // |done_cb| when completed.
   void DoStop(const PipelineStatusCB& done_cb);
   void OnStopCompleted(PipelineStatus status);
 
-  void OnAudioUnderflow();
-
   // Collection of callback methods and helpers for tracking changes in
   // buffering state and transition from paused/underflow states and playing
   // states.
   //
   // While in the kPlaying state:
   //   - A waiting to non-waiting transition indicates preroll has completed
   //     and StartPlayback() should be called
   //   - A non-waiting to waiting transition indicates underflow has occurred
-  //     and StartWaitingForEnoughData() should be called
+  //     and PausePlayback() should be called
   void BufferingStateChanged(BufferingState* buffering_state,
                              BufferingState new_buffering_state);
   bool WaitingForEnoughData() const;
-  void StartWaitingForEnoughData();
+  void TransitionToWaiting();
+  void TransitionToNonWaiting();
+  void PausePlayback();
   void StartPlayback();
 
   void StartClockIfWaitingForTimeUpdate_Locked();
 
   // Task runner used to execute pipeline tasks.
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   // MediaLog to which to log events.
   scoped_refptr<MediaLog> media_log_;
 
@@ skipping 87 matching lines @@
   scoped_ptr<SerialRunner> pending_callbacks_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(Pipeline);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_PIPELINE_H_