DevTools: Prepare for recursive viewport in datagrid

Source/devtools/front_end/DataGrid.js

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *        notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *        notice, this list of conditions and the following disclaimer in the
@@ skipping 1150 matching lines @@
     this.children = [];
     this.dataGrid = null;
     this.parent = null;
     /** @type {?WebInspector.DataGridNode} */
     this.previousSibling = null;
     /** @type {?WebInspector.DataGridNode} */
     this.nextSibling = null;
     this.disclosureToggleWidth = 10;
 }
 
+WebInspector.DataGridNode.NodeShallowHeight = 16;
+
 WebInspector.DataGridNode.prototype = {
     /** @type {boolean} */
     selectable: true,
 
     /** @type {boolean} */
     _isRoot: false,
 
     get element()
     {
         if (this._element)
@@ skipping 206 matching lines @@
         }
 
         return cell;
     },
 
     /**
      * @return {number}
      */
     nodeHeight: function()
     {
-        var rowHeight = 16;
+        var rowHeight = WebInspector.DataGridNode.NodeShallowHeight;
         if (!this.revealed)
             return 0;
         if (!this.expanded)
             return rowHeight;
         var result = rowHeight;
         for (var i = 0; i < this.children.length; i++)
             result += this.children[i].nodeHeight();
         return result;
     },
 
@@ skipping 410 matching lines @@
 
 WebInspector.CreationDataGridNode.prototype = {
     makeNormal: function()
     {
         delete this.isCreationNode;
         delete this.makeNormal;
     },
 
     __proto__: WebInspector.DataGridNode.prototype
 }