Remove unused ModalDialogDelegate class.

chrome/browser/ui/views/modal_dialog_delegate.h

-// Copyright (c) 2010 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_VIEWS_MODAL_DIALOG_DELEGATE_H_
-#define CHROME_BROWSER_UI_VIEWS_MODAL_DIALOG_DELEGATE_H_
-#pragma once
-
-#include "views/window/dialog_delegate.h"
-
-namespace views {
-class Window;
-}
-
-class ModalDialogDelegate : public views::DialogDelegate {
- public:
-  virtual ~ModalDialogDelegate() {}
-  // Methods called from AppModalDialog.
-  virtual gfx::NativeWindow GetDialogRootWindow() = 0;
-  virtual void ShowModalDialog();
-  virtual void ActivateModalDialog();
-  virtual void CloseModalDialog();
- protected:
-  ModalDialogDelegate();
-
-  // The dialog if it is currently visible.
-  views::Window* dialog_;
-};
-
-#endif  // CHROME_BROWSER_UI_VIEWS_MODAL_DIALOG_DELEGATE_H_
-