Closing simulation window in chromeos sessions causes crash.

ash/devtools/ash_devtools_dom_agent.h

 // Copyright 2016 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.
 
 #ifndef ASH_DEVTOOLS_ASH_DEVTOOLS_DOM_AGENT_H_
 #define ASH_DEVTOOLS_ASH_DEVTOOLS_DOM_AGENT_H_
 
 #include "ash/ash_export.h"
 #include "ash/devtools/ui_element_delegate.h"
 #include "base/macros.h"
@@ skipping 38 matching lines @@
   // UIElementDelegate:
   void OnUIElementAdded(UIElement* parent, UIElement* child) override;
   void OnUIElementReordered(UIElement* parent, UIElement* child) override;
   void OnUIElementRemoved(UIElement* ui_element) override;
   void OnUIElementBoundsChanged(UIElement* ui_element) override;
   bool IsHighlightingWindow(aura::Window* window) override;
 
   void AddObserver(AshDevToolsDOMAgentObserver* observer);
   void RemoveObserver(AshDevToolsDOMAgentObserver* observer);
   UIElement* GetElementFromNodeId(int node_id);
-  UIElement* window_element_root() const { return window_element_root_; };
+  UIElement* window_element_root() const { return window_element_root_.get(); };
 
  private:
   void OnNodeBoundsChanged(int node_id);
 
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildInitialTree();
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildTreeForUIElement(
       UIElement* ui_element);
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildTreeForWindow(
       UIElement* window_element_root,
       aura::Window* window);
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildTreeForRootWidget(
       UIElement* widget_element,
       views::Widget* widget);
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildTreeForView(
       UIElement* view_element,
       views::View* view);
   void RemoveDomNode(UIElement* ui_element);
   void Reset();
   void InitializeHighlightingWidget();
   void UpdateHighlight(
       const std::pair<aura::Window*, gfx::Rect>& window_and_bounds,
       SkColor background,
       SkColor border);
   ui::devtools::protocol::Response HighlightNode(
       std::unique_ptr<ui::devtools::protocol::DOM::HighlightConfig>
           highlight_config,
       int node_id);
 
   bool is_building_tree_;
-  UIElement* window_element_root_;
+  std::unique_ptr<UIElement> window_element_root_;
   std::unordered_map<int, UIElement*> node_id_to_ui_element_;
   std::unique_ptr<views::Widget> widget_for_highlighting_;
   base::ObserverList<AshDevToolsDOMAgentObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AshDevToolsDOMAgent);
 };
 
 }  // namespace devtools
 }  // namespace ash
 
 #endif  // ASH_DEVTOOLS_ASH_DEVTOOLS_DOM_AGENT_H_