DevTools: migrate treeoutline from hasChildren to is/setExpandable().

Source/devtools/front_end/network/XMLView.js

 // 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.
 
 /**
  * @constructor
  * @extends {WebInspector.View}
  * @param {!Document} parsedXML
  */
 WebInspector.XMLView = function(parsedXML)
@@ skipping 29 matching lines @@
 }
 
 /**
  * @constructor
  * @extends {TreeElement}
  * @param {!Node} node
  * @param {boolean} closeTag
  */
 WebInspector.XMLView.Node = function(node, closeTag)
 {
-    TreeElement.call(this, "", true);
+    TreeElement.call(this, "", !closeTag && !!node.childElementCount);
     this._node = node;
     this._closeTag = closeTag;
-    this._populated = false;
     this.selectable = false;
-    this.hasChildren = !closeTag && !!node.childElementCount;
     this._updateTitle();
 }
 
 /**
  * @param {!TreeOutline|!TreeElement} root
  * @param {!Node} xmlNode
  */
 WebInspector.XMLView.Node.populate = function(root, xmlNode)
 {
     var node = xmlNode.firstChild;
@@ skipping 90 matching lines @@
         this._updateTitle();
     },
 
     oncollapse: function()
     {
         this._updateTitle();
     },
 
     onpopulate: function()
     {
-        if (this._populated || this._closeTag)
-            return;
         WebInspector.XMLView.Node.populate(this, this._node);
         this.appendChild(new WebInspector.XMLView.Node(this._node, true));
-        this._populated = true;
     },
 
     __proto__: TreeElement.prototype
 }