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

chrome/browser/tab_contents/chrome_interstitial_page.cc

-// 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.
-
-#include "chrome/browser/tab_contents/chrome_interstitial_page.h"
-
-#include "chrome/browser/profiles/profile.h"
-#include "chrome/browser/renderer_preferences_util.h"
-#include "chrome/common/render_messages.h"
-#include "content/browser/renderer_host/render_view_host.h"
-#include "content/public/browser/web_contents.h"
-
-using content::WebContents;
-
-ChromeInterstitialPage::ChromeInterstitialPage(WebContents* tab,
-                                               bool new_navigation,
-                                               const GURL& url)
-    : InterstitialPage(tab, new_navigation, url) {
-  Profile* profile = Profile::FromBrowserContext(tab->GetBrowserContext());
-  content::RendererPreferences prefs;
-  renderer_preferences_util::UpdateFromSystemSettings(&prefs, profile);
-  set_renderer_preferences(prefs);
-}
-
-ChromeInterstitialPage::~ChromeInterstitialPage() {
-}
-
-void ChromeInterstitialPage::Show() {
-  InterstitialPage::Show();
-
-  render_view_host()->Send(
-      new ChromeViewMsg_SetAsInterstitial(render_view_host()->routing_id()));
-}