DevTools: do not allow using 'this' before call into super.

third_party/WebKit/Source/devtools/front_end/sdk/ProfileTreeModel.js

 // Copyright 2016 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.
 
 /**
  * @constructor
  * @param {!RuntimeAgent.CallFrame} callFrame
  */
 WebInspector.ProfileNode = function(callFrame)
 {
@@ skipping 50 matching lines @@
      * @return {number}
      */
     get columnNumber()
     {
         return this.callFrame.columnNumber;
     }
 };
 
 /**
  * @constructor
- * @param {!WebInspector.ProfileNode} root
  */
-WebInspector.ProfileTreeModel = function(root)
+WebInspector.ProfileTreeModel = function()
 {
-    this.root = root;
-    this._assignDepthsAndParents();
-    this.total = this._calculateTotals(this.root);
 };
 
 WebInspector.ProfileTreeModel.prototype = {
+    /**
+     * @param {!WebInspector.ProfileNode} root
+     * @protected
+     */
+    initialize: function(root)
+    {
+        this.root = root;
+        this._assignDepthsAndParents();
+        this.total = this._calculateTotals(this.root);
+    },
+
     _assignDepthsAndParents: function()
     {
         var root = this.root;
         root.depth = -1;
         root.parent = null;
         this.maxDepth = 0;
         var nodesToTraverse = [root];
         while (nodesToTraverse.length) {
             var parent = nodesToTraverse.pop();
             var depth = parent.depth + 1;
@@ skipping 25 matching lines @@
             dfsList.push(node);
             nodesToTraverse.push(...node.children);
         }
         while (dfsList.length > 1) {
             var node = dfsList.pop();
             node.parent.total += node.total;
         }
         return root.total;
     }
 };