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

Source/devtools/front_end/HeapSnapshot.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 copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 654 matching lines @@
         var retainingNodes = this._retainingNodes = new Uint32Array(this._edgeCount);
         var retainingEdges = this._retainingEdges = new Uint32Array(this._edgeCount);
         // Index of the first retainer in the _retainingNodes and _retainingEdges
         // arrays. Addressed by retained node index.
         var firstRetainerIndex = this._firstRetainerIndex = new Uint32Array(this.nodeCount + 1);
 
         var containmentEdges = this._containmentEdges;
         var edgeFieldsCount = this._edgeFieldsCount;
         var nodeFieldCount = this._nodeFieldCount;
         var edgeToNodeOffset = this._edgeToNodeOffset;
-        var nodes = this._nodes;
         var firstEdgeIndexes = this._firstEdgeIndexes;
         var nodeCount = this.nodeCount;
 
         for (var toNodeFieldIndex = edgeToNodeOffset, l = containmentEdges.length; toNodeFieldIndex < l; toNodeFieldIndex += edgeFieldsCount) {
             var toNodeIndex = containmentEdges[toNodeFieldIndex];
             if (toNodeIndex % nodeFieldCount)
                 throw new Error("Invalid toNodeIndex " + toNodeIndex);
             ++firstRetainerIndex[toNodeIndex / nodeFieldCount];
         }
         for (var i = 0, firstUnusedRetainerSlot = 0; i < nodeCount; i++) {
@@ skipping 231 matching lines @@
      */
     _bfs: function(nodesToVisit, nodesToVisitLength, distances)
     {
         // Preload fields into local variables for better performance.
         var edgeFieldsCount = this._edgeFieldsCount;
         var nodeFieldCount = this._nodeFieldCount;
         var containmentEdges = this._containmentEdges;
         var firstEdgeIndexes = this._firstEdgeIndexes;
         var edgeToNodeOffset = this._edgeToNodeOffset;
         var edgeTypeOffset = this._edgeTypeOffset;
-        var nodes = this._nodes;
         var nodeCount = this.nodeCount;
         var containmentEdgesLength = containmentEdges.length;
         var edgeWeakType = this._edgeWeakType;
         var noDistance = this._noDistance;
 
         var index = 0;
         while (index < nodesToVisitLength) {
             var nodeIndex = nodesToVisit[index++]; // shift generates too much garbage.
             var nodeOrdinal = nodeIndex / nodeFieldCount;
             var distance = distances[nodeOrdinal] + 1;
@@ skipping 912 matching lines @@
                 return indexA - indexB;
             return result;
         }
 
         this._iterationOrder.sortRange(sortByComparator, leftBound, rightBound, windowLeft, windowRight);
     },
 
     __proto__: WebInspector.HeapSnapshotFilteredOrderedIterator.prototype
 }