Include HTMLFrameOwnerElement.h in fewer headers

Source/core/dom/ChildFrameDisconnector.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 ChildFrameDisconnector_h
 #define ChildFrameDisconnector_h
 
-#include "core/dom/Node.h"
-#include "core/html/HTMLFrameOwnerElement.h"
 #include "platform/heap/Handle.h"
 
 namespace WebCore {
 
+class ElementShadow;
+class HTMLFrameOwnerElement;
+class Node;
+
 class ChildFrameDisconnector {
     STACK_ALLOCATED();
 public:
     enum DisconnectPolicy {
         RootAndDescendants,
         DescendantsOnly
     };
 
     explicit ChildFrameDisconnector(Node& root)
         : m_root(root)
     {
     }
 
     void disconnect(DisconnectPolicy = RootAndDescendants);
 
 private:
     void collectFrameOwners(Node&);
     void collectFrameOwners(ElementShadow&);
     void disconnectCollectedFrameOwners();
 
     WillBeHeapVector<RefPtrWillBeMember<HTMLFrameOwnerElement>, 10> m_frameOwners;
     Node& m_root;
 };
 
 } // namespace WebCore
 
 #endif // ChildFrameDisconnector_h