Have SourceBufferList trace all its object references.

Source/modules/mediasource/SourceBufferList.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "modules/mediasource/SourceBufferList.h"
 
+#include "core/dom/ExecutionContext.h"
 #include "core/events/GenericEventQueue.h"
 #include "modules/EventModules.h"
 #include "modules/mediasource/SourceBuffer.h"
 
 namespace blink {
 
 SourceBufferList::SourceBufferList(ExecutionContext* context, GenericEventQueue* asyncEventQueue)
     : m_executionContext(context)
     , m_asyncEventQueue(asyncEventQueue)
 {
@@ skipping 48 matching lines @@
     return EventTargetNames::SourceBufferList;
 }
 
 ExecutionContext* SourceBufferList::executionContext() const
 {
     return m_executionContext;
 }
 
 void SourceBufferList::trace(Visitor* visitor)
 {
+    visitor->trace(m_executionContext);
+    visitor->trace(m_asyncEventQueue);
     visitor->trace(m_list);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink