DevTools: better error handling in paint profiler UI

Source/devtools/front_end/layers/LayerPaintProfilerView.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
  * @param {function(!WebInspector.Layer, string=)} showImageForLayerCallback
  * @extends {WebInspector.SplitWidget}
  */
 WebInspector.LayerPaintProfilerView = function(showImageForLayerCallback)
@@ skipping 29 matching lines @@
             snapshot.commandLog(onCommandLogDone.bind(this, snapshot));
         }
 
         /**
          * @param {!WebInspector.PaintProfilerSnapshot=} snapshot
          * @param {!Array.<!Object>=} log
          * @this {WebInspector.LayerPaintProfilerView}
          */
         function onCommandLogDone(snapshot, log)
         {
-            this._logTreeView.setCommandLog(snapshot.target(), log);
+            this._logTreeView.setCommandLog(snapshot.target(), log || []);
             this._paintProfilerView.setSnapshotAndLog(snapshot || null, log || [], null);
         }
     },
 
     _onWindowChanged: function()
     {
         var window = this._paintProfilerView.windowBoundaries();
         this._logTreeView.updateWindow(window.left, window.right);
     },
 
     /**
      * @param {string=} imageURL
      */
     _showImage: function(imageURL)
     {
         this._showImageForLayerCallback(this._layer, imageURL);
     },
 
     __proto__: WebInspector.SplitWidget.prototype
 };