Make "three snapshot technique" work on heap snapshots loaded from files

Source/devtools/front_end/HeapSnapshotProxy.js

 /*
  * Copyright (C) 2011 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 copyrightdd
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 460 matching lines @@
     createNodesProviderForClass: function(className, aggregatesKey)
     {
         return this.callFactoryMethod(null, "createNodesProviderForClass", WebInspector.HeapSnapshotProviderProxy, className, aggregatesKey);
     },
 
     createNodesProviderForDominator: function(nodeIndex)
     {
         return this.callFactoryMethod(null, "createNodesProviderForDominator", WebInspector.HeapSnapshotProviderProxy, nodeIndex);
     },
 
+    maxJsNodeId: function(callback)
+    {
+        this.callMethod(callback, "maxJsNodeId");
+    },
+
     allocationTracesTops: function(callback)
     {
         this.callMethod(callback, "allocationTracesTops");
     },
 
     allocationNodeCallers: function(nodeId, callback)
     {
         this.callMethod(callback, "allocationNodeCallers", nodeId);
     },
 
@@ skipping 62 matching lines @@
     },
 
     sortAndRewind: function(comparator, callback)
     {
         this.callMethod(callback, "sortAndRewind", comparator);
     },
 
     __proto__: WebInspector.HeapSnapshotProxyObject.prototype
 }