[Panels] Fix browser crash when killing extension on Windows.

chrome/browser/ui/panels/panel_view.h

 // Copyright (c) 2012 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 CHROME_BROWSER_UI_PANELS_PANEL_VIEW_H_
 #define CHROME_BROWSER_UI_PANELS_PANEL_VIEW_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/ui/panels/native_panel.h"
 #include "ui/base/animation/animation_delegate.h"
@@ skipping 132 matching lines @@
   // |attribute_index|. This is used to update the style or extended style
   // for the native window.
   void UpdateWindowAttribute(int attribute_index,
                              int attribute_value,
                              bool to_set);
 #endif
 
   scoped_ptr<Panel> panel_;
   gfx::Rect bounds_;
 
-  // The window that holds all panel views.
+  // The window that holds all panel views. Lifetime managed by native widget.
+  // See widget.h.
   views::Widget* window_;
 
-  // The view hosting the web contents.
+  // The view hosting the web contents. Will be destroyed when child views
+  // of this class are destroyed.
   views::WebView* web_view_;
 
   // True if the panel should always stay on top of other windows.
   bool always_on_top_;
 
   // Is the panel receiving the focus?
   bool focused_;
 
   // Is the mouse button currently down?
   bool mouse_pressed_;
@@ skipping 24 matching lines @@
 
 #if defined(OS_WIN) && !defined(USE_ASH) && !defined(USE_AURA)
   // Used to provide custom taskbar thumbnail for Windows 7 and later.
   scoped_ptr<TaskbarWindowThumbnailerWin> thumbnailer_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(PanelView);
 };
 
 #endif  // CHROME_BROWSER_UI_PANELS_PANEL_VIEW_H_