Fix the crash of DisplayErrorDialog.

ash/display/display_error_dialog.h

Index: ash/display/display_error_dialog.h
diff --git a/ash/display/display_error_dialog.h b/ash/display/display_error_dialog.h
index 370a647080a56ac05a72fd5aa24c1a6c39cb2433..cd7829ea7caf4e03fde14049eabfb76715d6088f 100644
--- a/ash/display/display_error_dialog.h
+++ b/ash/display/display_error_dialog.h
@@ -5,8 +5,10 @@
 #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 {
@@ -27,13 +29,18 @@ 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();
 
@@ -49,6 +56,9 @@ class DisplayErrorDialog : public views::DialogDelegateView,
   // 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);