Adds a CancellableTaskFactory and exposes postLoadingTasks to Blink

Source/wtf/WeakPtr.h

 /*
  * Copyright (C) 2013 Google, Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 122 matching lines @@
     WeakPtr<T> createWeakPtr() { return WeakPtr<T>(m_ref); }
 
     void revokeAll()
     {
         T* ptr = m_ref->get();
         m_ref->clear();
         // We create a new WeakReference so that future calls to createWeakPtr() create nonzero WeakPtrs.
         m_ref = WeakReference<T>::create(ptr);
     }
 
+    bool hasWeakPtrs() const
+    {
+        return m_ref->refCount() > 1;
+    }
+
 private:
     RefPtr<WeakReference<T>> m_ref;
 };
 
 } // namespace WTF
 
 using WTF::WeakPtr;
 using WTF::WeakPtrFactory;
 using WTF::WeakReference;
 
 #endif