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

Source/modules/indexeddb/IDBTransaction.h

Index: Source/modules/indexeddb/IDBTransaction.h
diff --git a/Source/modules/indexeddb/IDBTransaction.h b/Source/modules/indexeddb/IDBTransaction.h
index f7531e38c39fd16d23241d9c573173ce37ca46e8..01709a7107bb644a42d801076fabcd6ccfd283aa 100644
--- a/Source/modules/indexeddb/IDBTransaction.h
+++ b/Source/modules/indexeddb/IDBTransaction.h
@@ -54,12 +54,12 @@ class IDBTransaction FINAL
     , public EventTargetWithInlineData
     , public ActiveDOMObject {
     DEFINE_EVENT_TARGET_REFCOUNTING(RefCountedGarbageCollected<IDBTransaction>);
-
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(IDBTransaction);
 public:
     static IDBTransaction* create(ExecutionContext*, int64_t, const Vector<String>& objectStoreNames, blink::WebIDBDatabase::TransactionMode, IDBDatabase*);
     static IDBTransaction* create(ExecutionContext*, int64_t, IDBDatabase*, IDBOpenDBRequest*, const IDBDatabaseMetadata& previousMetadata);
     virtual ~IDBTransaction();
-    void trace(Visitor*);
+    virtual void trace(Visitor*) OVERRIDE;
 
     static const AtomicString& modeReadOnly();
     static const AtomicString& modeReadWrite();