Oilpan: Prepare to move EventDispatchMediator to Oilpan heap.

Source/core/events/EventDispatcher.h

Index: Source/core/events/EventDispatcher.h
diff --git a/Source/core/events/EventDispatcher.h b/Source/core/events/EventDispatcher.h
index f753adc82aef3da3466009619530c36fa6cfbd78..891a9b9646e19e0b325501bd2446dc3a928078a9 100644
--- a/Source/core/events/EventDispatcher.h
+++ b/Source/core/events/EventDispatcher.h
@@ -48,8 +48,8 @@ enum EventDispatchContinuation {
 class EventDispatcher {
     STACK_ALLOCATED();
 public:
-    static bool dispatchEvent(Node*, PassRefPtr<EventDispatchMediator>);
-    static void dispatchScopedEvent(Node*, PassRefPtr<EventDispatchMediator>);
+    static bool dispatchEvent(Node*, PassRefPtrWillBeRawPtr<EventDispatchMediator>);
+    static void dispatchScopedEvent(Node*, PassRefPtrWillBeRawPtr<EventDispatchMediator>);
 
     static void dispatchSimulatedClick(Node*, Event* underlyingEvent, SimulatedClickMouseEventOptions);