Move PlatformEventDispatcher implementations to the Oilpan heap.

Source/core/frame/PlatformEventDispatcher.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PlatformEventDispatcher_h
 #define PlatformEventDispatcher_h
 
 #include "platform/heap/Handle.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 class PlatformEventController;
 
-class PlatformEventDispatcher {
+class PlatformEventDispatcher : public GarbageCollectedMixin {
 public:
     void addController(PlatformEventController*);
     void removeController(PlatformEventController*);
 
+    virtual void trace(Visitor*);
+
 protected:
     PlatformEventDispatcher();
-    virtual ~PlatformEventDispatcher();
 
     void notifyControllers();
 
     virtual void startListening() = 0;
     virtual void stopListening() = 0;
 
 private:
     void purgeControllers();
 
-    WillBePersistentHeapVector<RawPtrWillBeMember<PlatformEventController> > m_controllers;
+    void clearWeakMembers(Visitor*);
+
+    HeapVector<PlatformEventController*> m_controllers;
     bool m_needsPurge;
     bool m_isDispatching;
 };
 
 } // namespace blink
 
 #endif // PlatformEventDispatcher_h