[PPAPI][MediaStream] Support configure for video input.

ppapi/cpp/media_stream_video_track.h

Index: ppapi/cpp/media_stream_video_track.h
diff --git a/ppapi/cpp/media_stream_video_track.h b/ppapi/cpp/media_stream_video_track.h
index 52a0551e81cd32586e92fb4bd1140066366238fc..268e031a209f1b45e713041495774348b5a1eb08 100644
--- a/ppapi/cpp/media_stream_video_track.h
+++ b/ppapi/cpp/media_stream_video_track.h
@@ -73,6 +73,9 @@ class MediaStreamVideoTrack : public Resource {
   /// completion of <code>Configure()</code>.
   ///
   /// @return An int32_t containing a result code from <code>pp_errors.h</code>.
+  /// Returns <code>PP_ERROR_INPROGRESS</code> if there is a pending call of
+  /// <code>Configure()</code> or <code>GetFrame()</code>, or the plugin
+  /// holds some frames which are not recycled with <code>RecycleFrame()</code>.
   int32_t Configure(const int32_t attributes[],
                     const CompletionCallback& callback);