Timeline: fix exception when updating tree view details and Events tree experiment is off

third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js

 // Copyright 2015 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.VBox}
  * @param {!WebInspector.TimelineModel} model
  */
 WebInspector.TimelineTreeView = function(model)
@@ skipping 167 matching lines @@
             var nodeA = /** @type {!WebInspector.TimelineTreeView.GridNode} */ (a);
             var nodeB = /** @type {!WebInspector.TimelineTreeView.GridNode} */ (b);
             var nameA = WebInspector.TimelineTreeView.eventNameForSorting(nodeA._profileNode.event);
             var nameB = WebInspector.TimelineTreeView.eventNameForSorting(nodeB._profileNode.event);
             return nameA.localeCompare(nameB);
         }
     },
 
     _updateDetailsForSelection: function()
     {
+        // FIXME: remove this as we implement details for all modes.
+        if (!this._detailsView)
+            return;
         var selectedNode = this._dataGrid.selectedNode ? /** @type {!WebInspector.TimelineTreeView.GridNode} */ (this._dataGrid.selectedNode)._profileNode : null;
         if (selectedNode === this._lastSelectedNode)
             return;
         this._lastSelectedNode = selectedNode;
         this._detailsView.element.removeChildren();
         if (!selectedNode || !this._showDetailsForNode(selectedNode)) {
             var banner = this._detailsView.element.createChild("div", "banner");
             banner.createTextChild(WebInspector.UIString("No details are available for current selection."));
         }
     },
@@ skipping 596 matching lines @@
          * @this {WebInspector.EventsTimelineTreeView}
          */
         function showDetails(fragment)
         {
             this._detailsView.element.appendChild(fragment);
         }
     },
 
     __proto__: WebInspector.TimelineTreeView.prototype
 }