Fix a race condition in MediaStreamAudioTrackHost.

content/renderer/pepper/pepper_media_stream_audio_track_host.h

Index: content/renderer/pepper/pepper_media_stream_audio_track_host.h
diff --git a/content/renderer/pepper/pepper_media_stream_audio_track_host.h b/content/renderer/pepper/pepper_media_stream_audio_track_host.h
index 348103c9928c55faa4c7beca1e0259b2347e07a4..e57ed44c2d39ffa976a100282e3d60966217e379 100644
--- a/content/renderer/pepper/pepper_media_stream_audio_track_host.h
+++ b/content/renderer/pepper/pepper_media_stream_audio_track_host.h
@@ -54,7 +54,8 @@ class PepperMediaStreamAudioTrackHost : public PepperMediaStreamTrackHostBase {
     void InitBuffers();
 
     // Send enqueue buffer message on the main thread.
-    void SendEnqueueBufferMessageOnMainThread(int32_t index);
+    void SendEnqueueBufferMessageOnMainThread(int32_t index,
+                                              int32_t buffers_init_count);
 
     // MediaStreamAudioSink overrides:
     // These two functions should be called on the audio thread.
@@ -92,12 +93,16 @@ class PepperMediaStreamAudioTrackHost : public PepperMediaStreamTrackHostBase {
     // Access only on the audio thread.
     uint32_t buffer_data_size_;
 
-    // A lock to protect the index queue |buffers_|.
+    // A lock to protect the index queue |buffers_|, |init_buffers_count_| and
+    // buffers in |host_->buffer_manager()|.
     base::Lock lock_;
 
     // A queue for free buffer indices.
     std::deque<int32_t> buffers_;
 
+    // Count of |InitBuffers()| calls.
+    int32_t init_buffers_count_;

[Anand Mistry (off Chromium), 2014/07/25 00:42:54]

To me, after reading the code, I think it would be clearer to call this
buffer_generation_ instead (or something like that).

[Peng, 2014/07/25 15:25:31]

Done.

+
     scoped_refptr<base::MessageLoopProxy> main_message_loop_proxy_;
 
     base::ThreadChecker audio_thread_checker_;