Bug 1264479: don't crash on disappearing data channels. r=bwc

MozReview-Commit-ID: 3DmM7teByR8

--HG--
extra : rebase_source : 238054d17ff624eb203f8352493cd2ce99e11402

media/webrtc/signaling/src/peerconnection/PeerConnectionImpl.cpp

@@ -1984,6 +1984,11 @@ PeerConnectionImpl::RemoveOldRemoteTracks(RefPtr<PeerConnectionObserver>& aPco)
     const std::string& streamId = removedTrack->GetStreamId();
     const std::string& trackId = removedTrack->GetTrackId();
 
+    if (removedTrack->GetMediaType() == SdpMediaSection::kApplication) {
+      // TODO do we need to notify content somehow here?
+      continue;
+    }
+
     RefPtr<RemoteSourceStreamInfo> info = mMedia->GetRemoteStreamById(streamId);
     if (!info) {
       MOZ_ASSERT(false, "A stream/track was removed that wasn't in PCMedia. "