Bug 1011214: Release OMX monitor when shutting down Encoder output drain thread r=jhlin

media/webrtc/signaling/src/media-conduit/WebrtcOMXH264VideoCodec.cpp

@@ -133,6 +133,8 @@ public:
     lock.NotifyAll(); // In case Run() is waiting.
 
     if (mThread != nullptr) {
+      MonitorAutoUnlock unlock(mMonitor);
+      CODEC_LOGD("OMXOutputDrain thread shutdown");
       mThread->Shutdown();
       mThread = nullptr;
     }