Set audio format before adding pepper sink to audio track.

content/renderer/pepper/pepper_media_stream_audio_track_host.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 CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
 #define CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
 
 #include <deque>
 
 #include "base/compiler_specific.h"
@@ skipping 34 matching lines @@
     // This function is called on the main thread.
     void EnqueueBuffer(int32_t index);
 
     // This function is called on the main thread.
     int32_t Configure(int32_t number_of_buffers, int32_t duration,
                       const ppapi::host::ReplyMessageContext& context);
 
     // Send a reply to the currently pending |Configure()| request.
     void SendConfigureReply(int32_t result);
 
+    // MediaStreamAudioSink overrides:
+    // These two functions should be called on the audio thread.
+    // NOTE: For this specific instance, |OnSetFormat()| is also called on the
+    // main thread. However, the call to |OnSetFormat()| happens before this
+    // sink is added to an audio track, also on the main thread, which should
+    // avoid any potential races.
+    void OnData(const media::AudioBus& audio_bus,
+                base::TimeTicks estimated_capture_time) override;
+    void OnSetFormat(const media::AudioParameters& params) override;
+
    private:
     // Initializes buffers on the main thread.
     void SetFormatOnMainThread(int bytes_per_second, int bytes_per_frame);
 
     void InitBuffers();
 
     // Send enqueue buffer message on the main thread.
     void SendEnqueueBufferMessageOnMainThread(int32_t index,
                                               int32_t buffers_generation);
 
-    // MediaStreamAudioSink overrides:
-    // These two functions should be called on the audio thread.
-    void OnData(const media::AudioBus& audio_bus,
-                base::TimeTicks estimated_capture_time) override;
-    void OnSetFormat(const media::AudioParameters& params) override;
-
     // Unowned host which is available during the AudioSink's lifespan.
     // It is mainly used in the main thread. But the audio thread will use
     // host_->buffer_manager() to read some buffer properties. It is safe
     // because the buffer_manager()'s properties will not be changed after
     // initialization.
     PepperMediaStreamAudioTrackHost* host_;
 
     // The estimated capture time of the first sample frame of audio. This is
     // used as the timebase to compute the buffer timestamps.
     // Access only on the audio thread.
@@ skipping 81 matching lines @@
   bool connected_;
 
   AudioSink audio_sink_;
 
   DISALLOW_COPY_AND_ASSIGN(PepperMediaStreamAudioTrackHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_