fix build when ffmpeg, libvpx and libwebm are disabled

content/renderer/media/media_recorder_handler.h

Index: content/renderer/media/media_recorder_handler.h
diff --git a/content/renderer/media/media_recorder_handler.h b/content/renderer/media/media_recorder_handler.h
index 8d9d7ee15de18f703c060cc3664239fa126f9f44..0c4f3a99a24071a1591bf6cd1d68ffd00f39a120 100644
--- a/content/renderer/media/media_recorder_handler.h
+++ b/content/renderer/media/media_recorder_handler.h
@@ -87,8 +87,10 @@ class CONTENT_EXPORT MediaRecorderHandler final
 
   ScopedVector<VideoTrackRecorder> video_recorders_;
 
+#if !defined(MEDIA_DISABLE_LIBWEBM)
   // Worker class doing the actual Webm Muxing work.
   scoped_ptr<media::WebmMuxer> webm_muxer_;
+#endif
 
   base::WeakPtrFactory<MediaRecorderHandler> weak_factory_;