Move PlatformEventDispatcher implementations to the Oilpan heap.

Source/core/frame/PlatformEventDispatcher.h

Index: Source/core/frame/PlatformEventDispatcher.h
diff --git a/Source/core/frame/PlatformEventDispatcher.h b/Source/core/frame/PlatformEventDispatcher.h
index d05ddc9fc5a8f342fba0326b303bcf1f017cac69..4536f42dc77cbdcea77d47228c38c73d60d1b2e3 100644
--- a/Source/core/frame/PlatformEventDispatcher.h
+++ b/Source/core/frame/PlatformEventDispatcher.h
@@ -11,14 +11,15 @@
 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();
 
@@ -28,7 +29,9 @@ protected:
 private:
     void purgeControllers();
 
-    WillBePersistentHeapVector<RawPtrWillBeMember<PlatformEventController> > m_controllers;
+    void clearWeakMembers(Visitor*);
+
+    HeapVector<PlatformEventController*> m_controllers;
     bool m_needsPurge;
     bool m_isDispatching;
 };