Adds DisplayErrorDialog to show the error message of the failure of mirroring to the users.

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
new file mode 100644
index 0000000000000000000000000000000000000000..0436aabd2c312d077cbb0aaf957635e5ad067ba4
--- /dev/null
+++ b/ash/display/display_error_dialog.h
@@ -0,0 +1,50 @@
+// 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 "base/compiler_specific.h"
+#include "ui/views/window/dialog_delegate.h"
+
+namespace gfx {
+class Size;
+}  // namespace gfx
+
+namespace views {
+class Label;
+}  // namespace views
+
+namespace ash {
+namespace internal {
+
+// Dialog to show error messages when it fails to change the display
+// configuration to mirroring.
+class DisplayErrorDialog : public views::DialogDelegateView {
+ public:
+  // Shows the dialog to show errors.
+  static void ShowDialog();
+
+ private:
+  DisplayErrorDialog();
+  virtual ~DisplayErrorDialog();
+
+  // views::DialogDelegate overrides:
+  virtual int GetDialogButtons() const OVERRIDE;
+
+  // views::WidgetDelegate overrides::
+  virtual ui::ModalType GetModalType() const OVERRIDE;
+  virtual views::View* GetContentsView() OVERRIDE;
+
+  // views::View overrides:
+  virtual gfx::Size GetPreferredSize() OVERRIDE;
+
+  views::Label* label_;
+  DISALLOW_COPY_AND_ASSIGN(DisplayErrorDialog);
+};
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_DISPLAY_DISPLAY_ERROR_DIALOG_H_