Revert 255617, due to it not tracking use of the link doctor page properly.

chrome/browser/ui/alternate_error_tab_observer.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_ALTERNATE_ERROR_TAB_OBSERVER_H_
+#define CHROME_BROWSER_UI_ALTERNATE_ERROR_TAB_OBSERVER_H_
+
+#include "base/prefs/pref_change_registrar.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+class Profile;
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
+// Per-tab class to implement alternate error page functionality.
+class AlternateErrorPageTabObserver
+    : public content::WebContentsObserver,
+      public content::NotificationObserver,
+      public content::WebContentsUserData<AlternateErrorPageTabObserver> {
+ public:
+  virtual ~AlternateErrorPageTabObserver();
+
+  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+
+ private:
+  explicit AlternateErrorPageTabObserver(content::WebContents* web_contents);
+  friend class content::WebContentsUserData<AlternateErrorPageTabObserver>;
+
+  // content::WebContentsObserver overrides:
+  virtual void RenderViewCreated(
+      content::RenderViewHost* render_view_host) OVERRIDE;
+
+  // content::NotificationObserver overrides:
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
+  // Internal helpers ----------------------------------------------------------
+
+  // Returns the server that can provide alternate error pages.  If the returned
+  // URL is empty, the default error page built into WebKit will be used.
+  GURL GetAlternateErrorPageURL() const;
+
+  void OnAlternateErrorPagesEnabledChanged();
+
+  // Send the alternate error page URL to the renderer.
+  void UpdateAlternateErrorPageURL(content::RenderViewHost* rvh);
+
+  Profile* profile_;
+  content::NotificationRegistrar registrar_;
+  PrefChangeRegistrar pref_change_registrar_;
+
+  DISALLOW_COPY_AND_ASSIGN(AlternateErrorPageTabObserver);
+};
+
+#endif  // CHROME_BROWSER_UI_ALTERNATE_ERROR_TAB_OBSERVER_H_