Switch AlternateErrorPageTabObserver to use WebContentsUserData.

chrome/browser/ui/tab_contents/tab_contents.h

 // Copyright (c) 2012 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_UI_TAB_CONTENTS_TAB_CONTENTS_H_
 #define CHROME_BROWSER_UI_TAB_CONTENTS_TAB_CONTENTS_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/public/browser/web_contents_observer.h"
 
-class AlternateErrorPageTabObserver;
 class AutocompleteHistoryManager;
 class AutofillExternalDelegate;
 class AutofillManager;
 class AutomationTabHelper;
 class BasePanelBrowserTest;
 class BlockedContentTabHelper;
 class BookmarkTabHelper;
 class Browser;
 class BrowserCommandsTabContentsCreator;
 class BrowserLauncherItemControllerContentsCreator;
@@ skipping 343 matching lines @@
 
   // Handles displaying a web intents picker to the user.
   scoped_ptr<WebIntentPickerController> web_intent_picker_controller_;
 
   scoped_ptr<ZoomController> zoom_controller_;
 
   // Per-tab observers ---------------------------------------------------------
   // (These provide no API for callers; objects that need to exist 1:1 with tabs
   // and silently do their thing live here.)
 
-  scoped_ptr<AlternateErrorPageTabObserver> alternate_error_page_tab_observer_;
   scoped_ptr<extensions::WebNavigationTabObserver> webnavigation_observer_;
   scoped_ptr<ExternalProtocolObserver> external_protocol_observer_;
   scoped_ptr<NavigationMetricsRecorder> navigation_metrics_recorder_;
   scoped_ptr<OmniboxSearchHint> omnibox_search_hint_;
 #if defined(ENABLE_ONE_CLICK_SIGNIN)
   scoped_ptr<OneClickSigninHelper> one_click_signin_helper_;
 #endif
   scoped_ptr<PDFTabObserver> pdf_tab_observer_;
   scoped_ptr<PepperBrokerObserver> pepper_broker_observer_;
   scoped_ptr<PluginObserver> plugin_observer_;
   scoped_ptr<printing::PrintPreviewMessageHandler> print_preview_;
   scoped_ptr<safe_browsing::SafeBrowsingTabObserver>
       safe_browsing_tab_observer_;
 
   // WebContents (MUST BE LAST) ------------------------------------------------
 
   // If true, we're running the destructor.
   bool in_destructor_;
 
   // The supporting objects need to outlive the WebContents dtor (as they may
   // be called upon during its execution). As a result, this must come last
   // in the list.
   scoped_ptr<content::WebContents> web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(TabContents);
 };
 
 #endif  // CHROME_BROWSER_UI_TAB_CONTENTS_TAB_CONTENTS_H_