Fix the crash of DisplayErrorDialog.

ash/display/display_error_dialog.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 ASH_DISPLAY_DISPLAY_ERROR_DIALOG_H_
 #define ASH_DISPLAY_DISPLAY_ERROR_DIALOG_H_
 
+#include "ash/ash_export.h"
 #include "ash/display/display_controller.h"
 #include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
 #include "ui/views/window/dialog_delegate.h"
 
 namespace aura {
 class RootWindow;
 }  // namespace aura
 
 namespace gfx {
 class Display;
 class Size;
 }  // namespace gfx
 
 namespace views {
 class Label;
 }  // namespace views
 
 namespace ash {
 namespace internal {
 
 // Dialog used to show an error messages when unable to change the display
 // configuration to mirroring.
-class DisplayErrorDialog : public views::DialogDelegateView,
-                           public ash::DisplayController::Observer {
+class ASH_EXPORT DisplayErrorDialog : public views::DialogDelegateView,
+                                      public ash::DisplayController::Observer {
  public:
   // Shows the error dialog.
   static void ShowDialog();
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(DisplayErrorDialogTest, Normal);
+  FRIEND_TEST_ALL_PREFIXES(DisplayErrorDialogTest, CallTwice);
+  FRIEND_TEST_ALL_PREFIXES(DisplayErrorDialogTest, SingleDisplay);
+  FRIEND_TEST_ALL_PREFIXES(DisplayErrorDialogTest, DisplayDisconnected);
+
   DisplayErrorDialog();
   virtual ~DisplayErrorDialog();
 
   // views::DialogDelegate overrides:
   virtual int GetDialogButtons() const OVERRIDE;
 
   // views::WidgetDelegate overrides::
   virtual ui::ModalType GetModalType() const OVERRIDE;
 
   // views::View overrides:
   virtual gfx::Size GetPreferredSize() OVERRIDE;
 
   // ash::DisplayController::Observer overrides:
   virtual void OnDisplayConfigurationChanging() OVERRIDE;
 
+  // Returns the pointer of the current instance of this dialog.
+  static DisplayErrorDialog* GetInstanceForTest();
+
   views::Label* label_;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayErrorDialog);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_DISPLAY_ERROR_DIALOG_H_