Oilpan: Move LifecycleNotifier's hierarchy to Oilpan's heap

Source/core/dom/ContextLifecycleNotifier.h

Index: Source/core/dom/ContextLifecycleNotifier.h
diff --git a/Source/core/dom/ContextLifecycleNotifier.h b/Source/core/dom/ContextLifecycleNotifier.h
index 178bf676ddc25d37917f03c261bbf2d8a4fd5fb1..2f6acc11b80796403cdd2586dcc33dd5334b882d 100644
--- a/Source/core/dom/ContextLifecycleNotifier.h
+++ b/Source/core/dom/ContextLifecycleNotifier.h
@@ -39,7 +39,7 @@ class ExecutionContext;
 
 class ContextLifecycleNotifier : public LifecycleNotifier<ExecutionContext> {
 public:
-    typedef HashSet<ActiveDOMObject*> ActiveDOMObjectSet;
+    typedef WillBeHeapHashSet<RawPtrWillBeWeakMember<ActiveDOMObject>> ActiveDOMObjectSet;
 
     const ActiveDOMObjectSet& activeDOMObjects() const { return m_activeDOMObjects; }
 
@@ -53,6 +53,8 @@ public:
     bool contains(ActiveDOMObject* object) const { return m_activeDOMObjects.contains(object); }
     bool hasPendingActivity() const;
 
+    virtual void trace(Visitor*) override;
+
 protected:
     explicit ContextLifecycleNotifier(ExecutionContext*);