Oilpan: switch some leftover raw references over to traced Member<>s.

Source/modules/mediastream/RTCDataChannel.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 316 matching lines @@
 void RTCDataChannel::clearWeakMembers(Visitor* visitor)
 {
     if (visitor->isHeapObjectAlive(m_connection))
         return;
     stop();
     m_connection = nullptr;
 }
 
 DEFINE_TRACE(RTCDataChannel)
 {
+    visitor->trace(m_executionContext);
     visitor->trace(m_scheduledEvents);
     visitor->template registerWeakMembers<RTCDataChannel, &RTCDataChannel::clearWeakMembers>(this);
     RefCountedGarbageCollectedEventTargetWithInlineData<RTCDataChannel>::trace(visitor);
 }
 
 } // namespace blink