DevTools: better error handling in paint profiler UI

Source/devtools/front_end/timeline/PaintProfilerView.js

 /*
  * Copyright (C) 2013 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 66 matching lines @@
     setSnapshotAndLog: function(snapshot, log, clipRect)
     {
         this._reset();
         this._snapshot = snapshot;
         this._log = log;
         this._logCategories = this._log.map(WebInspector.PaintProfilerView._categoryForLogItem);
 
         if (!this._snapshot) {
             this._update();
             this._pieChart.setTotal(0);
+            this._selectionWindow.setEnabled(false);
             return;
         }
+        this._selectionWindow.setEnabled(true);
         this._progressBanner.classList.remove("hidden");
         snapshot.requestImage(null, null, 1, this._showImageCallback);
         snapshot.profile(clipRect, onProfileDone.bind(this));
         /**
          * @param {!Array.<!LayerTreeAgent.PaintProfile>=} profiles
          * @this {WebInspector.PaintProfilerView}
          */
         function onProfileDone(profiles)
         {
             this._progressBanner.classList.add("hidden");
@@ skipping 165 matching lines @@
     this._treeOutline.element.addEventListener("mousemove", this._onMouseMove.bind(this), false);
     this._treeOutline.element.addEventListener("mouseout", this._onMouseMove.bind(this), false);
     this._treeOutline.element.addEventListener("contextmenu", this._onContextMenu.bind(this), true);
 
     this._reset();
 }
 
 WebInspector.PaintProfilerCommandLogView.prototype = {
     /**
      * @param {?WebInspector.Target} target
-     * @param {!Array.<!WebInspector.PaintProfilerLogItem>=} log
+     * @param {!Array.<!WebInspector.PaintProfilerLogItem>} log
      */
     setCommandLog: function(target, log)
     {
         this._target = target;
         this._log = log;
         this.updateWindow();
     },
 
     /**
       * @param {!TreeOutline} treeOutline
       * @param {!WebInspector.PaintProfilerLogItem} logItem
       */
     _appendLogItem: function(treeOutline, logItem)
     {
         var treeElement = new WebInspector.LogTreeElement(this, logItem);
         treeOutline.appendChild(treeElement);
     },
 
     /**
      * @param {number=} stepLeft
      * @param {number=} stepRight
      */
     updateWindow: function(stepLeft, stepRight)
     {
         this._treeOutline.removeChildren();
-        if (!this._log)
+        if (!this._log.length)
             return;
         stepLeft = stepLeft || 0;
         stepRight = stepRight || this._log.length;
         for (var i = stepLeft; i < stepRight; ++i)
             this._appendLogItem(this._treeOutline, this._log[i]);
     },
 
     _reset: function()
     {
         this._log = [];
@@ skipping 273 matching lines @@
     var method = logItem.method.toTitleCase();
 
     var logItemCategories = WebInspector.PaintProfilerView._initLogItemCategories();
     var result = logItemCategories[method];
     if (!result) {
         result = WebInspector.PaintProfilerView.categories()["misc"];
         logItemCategories[method] = result;
     }
     return result;
 }