Support configuring the audio buffer duration in the Pepper MediaStream API.

ppapi/shared_impl/media_stream_audio_track_shared.h

Index: ppapi/shared_impl/media_stream_audio_track_shared.h
diff --git a/ppapi/shared_impl/media_stream_audio_track_shared.h b/ppapi/shared_impl/media_stream_audio_track_shared.h
index 0a2ecea69dbfa70cf1488dd460134bd70484cd6c..8d9cbe5d84e41cee53a893da1d3b56eef479f434 100644
--- a/ppapi/shared_impl/media_stream_audio_track_shared.h
+++ b/ppapi/shared_impl/media_stream_audio_track_shared.h
@@ -13,8 +13,9 @@ namespace ppapi {
 class PPAPI_SHARED_EXPORT MediaStreamAudioTrackShared {
  public:
   struct Attributes {
-    Attributes() : buffers(0) {}
+    Attributes() : buffers(0), duration(0) {}
     int32_t buffers;
+    int32_t duration;
   };
 
   static bool VerifyAttributes(const Attributes& attributes);