Use InterstitialPage through a delegate interface instead of deriving from it.

chrome/browser/tab_contents/chrome_interstitial_page.h

-// Copyright (c) 2011 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_TAB_CONTENTS_CHROME_INTERSTITIAL_PAGE_H_
-#define CHROME_BROWSER_TAB_CONTENTS_CHROME_INTERSTITIAL_PAGE_H_
-#pragma once
-
-#include <map>
-#include <string>
-
-#include "content/browser/tab_contents/interstitial_page.h"
-#include "content/public/browser/notification_observer.h"
-#include "googleurl/src/gurl.h"
-
-// This class adds the possibility to react to DOMResponse-messages sent by
-// the RenderViewHost via ChromeRenderViewHostObserver to the InterstitialPage.
-class ChromeInterstitialPage : public InterstitialPage {
- public:
-  ChromeInterstitialPage(content::WebContents* tab,
-                         bool new_navigation,
-                         const GURL& url);
-  virtual ~ChromeInterstitialPage();
-
-  // Shows the interstitial page in the tab.
-  virtual void Show() OVERRIDE;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ChromeInterstitialPage);
-};
-
-#endif  // CHROME_BROWSER_TAB_CONTENTS_CHROME_INTERSTITIAL_PAGE_H_