DevTools: better error handling in paint profiler UI

Source/devtools/front_end/timeline/TimelinePaintProfilerView.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 {!WebInspector.TracingTimelineFrameModel} frameModel
  * @extends {WebInspector.SplitWidget}
  */
 WebInspector.TimelinePaintProfilerView = function(frameModel)
@@ skipping 74 matching lines @@
         /**
          * @param {?DOMAgent.Rect} tileRect
          * @param {?WebInspector.PaintProfilerSnapshot} snapshot
          * @this WebInspector.TimelinePaintProfilerView
          */
         function onSnapshotLoaded(tileRect, snapshot)
         {
             this._disposeSnapshot();
             this._lastLoadedSnapshot = snapshot;
             this._imageView.setMask(tileRect);
-            if (!snapshot)
+            if (!snapshot) {
+                this._imageView.showImage();
                 return;
+            }
             snapshot.commandLog(onCommandLogDone.bind(this, snapshot, tileRect));
         }
 
         /**
          * @param {!WebInspector.PaintProfilerSnapshot} snapshot
          * @param {?DOMAgent.Rect} clipRect
          * @param {!Array.<!WebInspector.PaintProfilerLogItem>=} log
          * @this {WebInspector.TimelinePaintProfilerView}
          */
         function onCommandLogDone(snapshot, clipRect, log)
         {
-            this._logTreeView.setCommandLog(snapshot.target(), log);
+            this._logTreeView.setCommandLog(snapshot.target(), log || []);
             this._paintProfilerView.setSnapshotAndLog(snapshot, log || [], clipRect);
         }
     },
 
     _disposeSnapshot: function()
     {
         if (!this._lastLoadedSnapshot)
             return;
         this._lastLoadedSnapshot.dispose();
         this._lastLoadedSnapshot = null;
@@ skipping 67 matching lines @@
         matrix = new WebKitCSSMatrix().translate(this._transformController.offsetX(), this._transformController.offsetY()).multiply(matrix);
         this._imageContainer.style.webkitTransform = matrix.toString();
     },
 
     /**
      * @param {string=} imageURL
      */
     showImage: function(imageURL)
     {
         this._imageContainer.classList.toggle("hidden", !imageURL);
-        this._imageElement.src = imageURL;
+        if (imageURL)
+            this._imageElement.src = imageURL;
     },
 
     /**
      * @param {?DOMAgent.Rect} maskRectangle
      */
     setMask: function(maskRectangle)
     {
         this._maskRectangle = maskRectangle;
         this._maskElement.classList.toggle("hidden", !maskRectangle);
     },
 
     __proto__: WebInspector.Widget.prototype
 };