Refactor the API for setting dynamic resource load priorities

Source/core/fetch/ResourceLoaderSet.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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 32 matching lines @@
     static ResourceLoaderSet* create();
     DECLARE_TRACE();
 
     void add(ResourceLoader* loader) { m_set.add(loader); }
     void remove(ResourceLoader* loader) { m_set.remove(loader); }
     bool isEmpty() const { return m_set.isEmpty(); }
     bool contains(ResourceLoader* loader) const { return m_set.contains(loader); }
     void cancelAll();
     void setAllDefersLoading(bool);
     int size() const { return m_set.size(); }
+    const HeapHashSet<Member<ResourceLoader>>& hashSet() const { return m_set; }
 
 private:
     SetType m_set;
 };
 
 }
 
 #endif