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

chrome/renderer/chrome_render_view_observer.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_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_
 #define CHROME_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_
 #pragma once
 
 #include <set>
 #include <string>
@@ skipping 118 matching lines @@
   void OnJavaScriptStressTestControl(int cmd, int param);
   void OnDownloadFavicon(int id, const GURL& image_url, int image_size);
   void OnSetIsPrerendering(bool is_prerendering);
   void OnSetAllowDisplayingInsecureContent(bool allow);
   void OnSetAllowRunningInsecureContent(bool allow);
   void OnSetClientSidePhishingDetection(bool enable_phishing_detection);
   void OnSetVisuallyDeemphasized(bool deemphasized);
   void OnStartFrameSniffer(const string16& frame_name);
   void OnGetFPS();
   void OnAddStrictSecurityHost(const std::string& host);
-  void OnSetAsInterstitial();
 
   // Captures the thumbnail and text contents for indexing for the given load
   // ID. If the view's load ID is different than the parameter, this call is
   // a NOP. Typically called on a timer, so the load ID may have changed in the
   // meantime.
   void CapturePageInfo(int load_id, bool preliminary_capture);
 
   // Retrieves the text from the given frame contents, the page text up to the
   // maximum amount kMaxIndexChars will be placed into the given buffer.
   void CaptureText(WebKit::WebFrame* frame, string16* contents);
@@ skipping 69 matching lines @@
   // ImageResourceFetchers schedule via DownloadImage.
   ImageResourceFetcherList image_fetchers_;
 
   // A color page overlay when visually de-emaphasized.
   scoped_ptr<WebViewColorOverlay> dimmed_color_overlay_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeRenderViewObserver);
 };
 
 #endif  // CHROME_RENDERER_CHROME_RENDER_VIEW_OBSERVER_H_