Oilpan: Allocate all EventTarget derived types on the manged heap.

Source/modules/mediasource/MediaSourceBase.h

Index: Source/modules/mediasource/MediaSourceBase.h
diff --git a/Source/modules/mediasource/MediaSourceBase.h b/Source/modules/mediasource/MediaSourceBase.h
index 9be374da4963a3f56322b9795728e36a596401f9..36c8b227d2cc0d1e814b45e4fd33f540c8313d12 100644
--- a/Source/modules/mediasource/MediaSourceBase.h
+++ b/Source/modules/mediasource/MediaSourceBase.h
@@ -50,7 +50,8 @@ class ExceptionState;
 class GenericEventQueue;
 
 class MediaSourceBase : public RefCountedWillBeRefCountedGarbageCollected<MediaSourceBase>, public HTMLMediaSource, public ActiveDOMObject, public EventTargetWithInlineData {
-    DEFINE_EVENT_TARGET_REFCOUNTING(RefCountedWillBeRefCountedGarbageCollected<MediaSourceBase>);
+    REFCOUNTED_EVENT_TARGET(MediaSourceBase);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(MediaSourceBase);
 public:
     static const AtomicString& openKeyword();
     static const AtomicString& closedKeyword();
@@ -89,8 +90,6 @@ public:
     // URLRegistrable interface
     virtual URLRegistry& registry() const OVERRIDE FINAL;
 
-    virtual void trace(Visitor*) { }
-
 protected:
     explicit MediaSourceBase(ExecutionContext*);