Bug 1318999 - Revoke MediaDataDecoder callback after RemoteVideoDecoder has been shut down. r=jya

--HG--
extra : rebase_source : 095eebbd7e2457a52aa7679d666ca10da3459259

dom/media/ipc/VideoDecoderChild.cpp

@@ -255,6 +255,7 @@ VideoDecoderChild::Shutdown()
     SendShutdown();
   }
   mInitialized = false;
+  mCallback = nullptr;
 }
 
 bool