Introduce InspectorIdentifiers<> and use it to assign/lookup LocalFrame and DocumentLoader

Source/core/dom/DOMNodeIds.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 DOMNodeIds_h
 #define DOMNodeIds_h
 
 #include "core/CoreExport.h"
+#include "core/dom/Node.h"
 #include "core/dom/WeakIdentifierMap.h"
 
 namespace blink {
 
-class Node;
-
 #if !ENABLE(OILPAN)
 template<> struct WeakIdentifierMapTraits<Node> {
     static void removedFromIdentifierMap(Node*);
     static void addedToIdentifierMap(Node*);
 };
 #endif
 
-typedef WeakIdentifierMap<Node> WeakNodeMap;
+extern template class WeakIdentifierMap<Node>;
+using WeakNodeMap = WeakIdentifierMap<Node>;
 
 class CORE_EXPORT DOMNodeIds {
 public:
     static int idForNode(Node*);
     static Node* nodeForId(int);
 };
 
 } // namespace blink
 
 
 #endif // DOMNodeIds_h