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

Source/core/workers/AbstractWorker.h

Index: Source/core/workers/AbstractWorker.h
diff --git a/Source/core/workers/AbstractWorker.h b/Source/core/workers/AbstractWorker.h
index 9abea7f7c510b7a32bd5766e9e364b85c9838af4..783d4890770376b1d48474af2a1ab921edeadeff 100644
--- a/Source/core/workers/AbstractWorker.h
+++ b/Source/core/workers/AbstractWorker.h
@@ -48,7 +48,8 @@ class KURL;
 class ExecutionContext;
 
 class AbstractWorker : public RefCountedWillBeRefCountedGarbageCollected<AbstractWorker>, public EventTargetWithInlineData, public ActiveDOMObject {
-    DEFINE_EVENT_TARGET_REFCOUNTING(RefCountedWillBeRefCountedGarbageCollected<AbstractWorker>);
+    REFCOUNTED_EVENT_TARGET(AbstractWorker);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(AbstractWorker);
 public:
     // EventTarget APIs
     virtual ExecutionContext* executionContext() const OVERRIDE FINAL { return ActiveDOMObject::executionContext(); }
@@ -58,8 +59,6 @@ public:
     AbstractWorker(ExecutionContext*);
     virtual ~AbstractWorker();
 
-    virtual void trace(Visitor*) { }
-
 protected:
     // Helper function that converts a URL to an absolute URL and checks the result for validity.
     KURL resolveURL(const String& url, ExceptionState&);