Enabling page visibility api in the chrome browser.

content/browser/tab_contents/tab_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 CONTENT_BROWSER_TAB_CONTENTS_TAB_CONTENTS_H_
 #define CONTENT_BROWSER_TAB_CONTENTS_TAB_CONTENTS_H_
 #pragma once
 
 #include <deque>
 #include <map>
@@ skipping 756 matching lines @@
                                 uint64 upload_position, uint64 upload_size);
   virtual bool IsExternalTabContainer() const;
   virtual void DidInsertCSS();
   virtual void FocusedNodeChanged(bool is_editable_node);
   virtual void UpdateZoomLimits(int minimum_percent,
                                 int maximum_percent,
                                 bool remember);
   virtual void WorkerCrashed();
   virtual void RequestDesktopNotificationPermission(const GURL& source_origin,
                                                     int callback_context);
+  virtual bool IsHidden() const OVERRIDE;
 
   // RenderViewHostManager::Delegate -------------------------------------------
 
   // Blocks/unblocks interaction with renderer process.
   void BlockTabContent(bool blocked);
 
   virtual void BeforeUnloadFiredFromRenderManager(
       bool proceed,
       bool* proceed_to_fire_unload);
   virtual void DidStartLoadingFromRenderManager(
@@ skipping 176 matching lines @@
   // remember it.
   bool temporary_zoom_settings_;
 
   // A list of observers notified when page state changes. Weak references.
   ObserverList<TabContentsObserver> observers_;
 
   // Content restrictions, used to disable print/copy etc based on content's
   // (full-page plugins for now only) permissions.
   int content_restrictions_;
 
+  // We need to know if the tab contents is hidden initially, before the
+  // delegate is set. This variable os only used in the call to IsHidden() if
+  // the delegate is NULL.
+  bool is_initially_hidden_;
+
   DISALLOW_COPY_AND_ASSIGN(TabContents);
 };
 
 #endif  // CONTENT_BROWSER_TAB_CONTENTS_TAB_CONTENTS_H_