Timeline: fix NPE in heavy stack view when clearing Timeline

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.
 
 /**
  * @unrestricted
  * @implements {UI.Searchable}
  */
 Timeline.TimelineTreeView = class extends UI.VBox {
   constructor() {
@@ skipping 222 matching lines @@
   }
 
   /**
    * @protected
    */
   refreshTree() {
     this._linkifier.reset();
     if (this._searchableView)
       this._searchableView.cancelSearch();
     this._dataGrid.rootNode().removeChildren();
-    if (!this._model)
+    if (!this._model) {
+      this._updateDetailsForSelection();
       return;
+    }
     this._root = this._buildTree();
     var children = this._root.children();
     var maxSelfTime = 0;
     var maxTotalTime = 0;
     for (var child of children.values()) {
       maxSelfTime = Math.max(maxSelfTime, child.selfTime);
       maxTotalTime = Math.max(maxTotalTime, child.totalTime);
     }
     for (var child of children.values()) {
       // Exclude the idle time off the total calculation.
@@ skipping 730 matching lines @@
 
   _onSelectionChanged() {
     this.dispatchEventToListeners(Timeline.TimelineStackView.Events.SelectionChanged);
   }
 };
 
 /** @enum {symbol} */
 Timeline.TimelineStackView.Events = {
   SelectionChanged: Symbol('SelectionChanged')
 };