[PPAPI] Pepper MediaStream API audio track implementation and example.

ppapi/shared_impl/media_stream_frame_buffer.h

Index: ppapi/shared_impl/media_stream_frame_buffer.h
diff --git a/ppapi/shared_impl/media_stream_frame_buffer.h b/ppapi/shared_impl/media_stream_frame_buffer.h
index e95084642c03bc20a2ae32b452df4f0a88ca8c4d..46cfee402e01fdada265ca9f6a8d6d7540f4b51b 100644
--- a/ppapi/shared_impl/media_stream_frame_buffer.h
+++ b/ppapi/shared_impl/media_stream_frame_buffer.h
@@ -38,8 +38,10 @@ class PPAPI_SHARED_EXPORT MediaStreamFrameBuffer {
   class PPAPI_SHARED_EXPORT Delegate {
    public:
     virtual ~Delegate();
-    // It is called when a new frame is enqueued.
-    virtual void OnNewFrameEnqueued();
+    // It is called before a new frame being enqueued. Return true if the frame
+    // is consumed by |Delegate|, and then the frame will not be added into the
+    // |frame_queue_|.
+    virtual bool OnNewFramePreEnqueued(int32_t index);

[yzshen1, 2014/01/29 21:28:06]

BeforeNewFrameEnqueued() may be more clearer.

That being said, I think the old way is easier to understand: we always enqueue
the frame index, and send a OnNewFrameEqueued() notification.
Why do we need such a change?

[Peng, 2014/01/31 18:54:43]

I though the performance is slightly better by avoiding an extra enqueue and
dequeue. Change it back. Done

   };
 
   // MediaStreamFrameBuffer doesn't own |delegate|, the caller should keep