Bug 1415556 - P2. Make member const. r=padenot

MozReview-Commit-ID: JPDW5cX8RvH

--HG--
extra : rebase_source : c83efd6665e23c89922d6d2cfdcd4f9ad3de3afa

dom/media/MediaStreamGraphImpl.h

@@ -780,7 +780,7 @@ public:
    * True when processing real-time audio/video.  False when processing non-realtime
    * audio.
    */
-  bool mRealtime;
+  const bool mRealtime;
   /**
    * True when a non-realtime MediaStreamGraph has started to process input.  This
    * value is only accessed on the main thread.