Enabling page visibility api in the chrome browser.

content/browser/tab_contents/tab_contents_delegate.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 "content/browser/tab_contents/tab_contents_delegate.h"
 
 #include "chrome/common/url_constants.h"
 #include "ui/gfx/rect.h"
 
 std::string TabContentsDelegate::GetNavigationHeaders(const GURL& url) {
@@ skipping 181 matching lines @@
 void TabContentsDelegate::ContentRestrictionsChanged(TabContents* source) {
 }
 
 bool TabContentsDelegate::ShouldShowHungRendererDialog() {
   return true;
 }
 
 void TabContentsDelegate::WorkerCrashed() {
 }
 
+bool TabContentsDelegate::IsHidden(const TabContents* source) const {
+  return false;
+}
+
 TabContentsDelegate::~TabContentsDelegate() {
 }