Enabling page visibility api in the chrome browser.

chrome/browser/prerender/prerender_contents.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_PRERENDER_PRERENDER_CONTENTS_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_CONTENTS_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 133 matching lines @@
   virtual int GetBrowserWindowID() const OVERRIDE;
   virtual void DidNavigate(
       RenderViewHost* render_view_host,
       const ViewHostMsg_FrameNavigate_Params& params) OVERRIDE;
   virtual void UpdateTitle(RenderViewHost* render_view_host,
                            int32 page_id,
                            const std::wstring& title);
   virtual WebPreferences GetWebkitPrefs() OVERRIDE;
   virtual void Close(RenderViewHost* render_view_host) OVERRIDE;
   virtual RendererPreferences GetRendererPrefs(Profile* profile) const OVERRIDE;
+  virtual bool IsHidden() const OVERRIDE;
 
   // TabContentsObserver implementation.
   virtual void DidStopLoading() OVERRIDE;
 
   // RenderViewHostDelegate::View
   // TODO(dominich): Remove when no longer a delegate for the view.
   virtual void CreateNewWindow(
       int route_id,
       const ViewHostMsg_CreateWindow_Params& params) OVERRIDE;
   virtual void CreateNewWidget(int route_id,
@@ skipping 172 matching lines @@
   scoped_ptr<TabContentsWrapper> prerender_contents_;
 
   scoped_ptr<PrerenderRenderViewHostObserver> render_view_host_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderContents);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_CONTENTS_H_