Move Event to oilpan's heap

Now there is no test failing when I change RefCounted<Event> to RefCountedGarbageCollected<Event>. Thus this CL does the change.

BUG=341032

Review URL: https://codereview.chromium.org/208173004

git-svn-id: svn://svn.chromium.org/blink/trunk@169941 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/events/Event.h

@@ -46,7 +46,7 @@ public:
     bool cancelable;
 };
 
-class Event : public RefCounted<Event>,  public ScriptWrappable {
+class Event : public RefCountedWillBeRefCountedGarbageCollected<Event>,  public ScriptWrappable {
 public:
     enum PhaseType {
         NONE                = 0,