Always install a BookmarkUndoService as a BookmarkModelObserver on iOS

chrome/browser/bookmarks/bookmark_model_factory.cc

 // 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.
 
 #include "chrome/browser/bookmarks/bookmark_model_factory.h"
 
 #include "base/command_line.h"
 #include "base/deferred_sequenced_task_runner.h"
 #include "base/memory/singleton.h"
 #include "base/prefs/pref_service.h"
@@ skipping 47 matching lines @@
       profile, OmniboxFieldTrial::BookmarksIndexURLsValue());
   bookmark_client->model()->Load(
       profile->GetPrefs(),
       profile->GetPrefs()->GetString(prefs::kAcceptLanguages),
       profile->GetPath(),
       StartupTaskRunnerServiceFactory::GetForProfile(profile)
           ->GetBookmarkTaskRunner(),
       content::BrowserThread::GetMessageLoopProxyForThread(
           content::BrowserThread::UI));
 #if !defined(OS_ANDROID)
-  if (CommandLine::ForCurrentProcess()->HasSwitch(
-     switches::kEnableBookmarkUndo)) {
+  bool register_bookmark_undo_service_as_observer = true;
+#if !defined(OS_IOS)
+  register_bookmark_undo_service_as_observer =
+      CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableBookmarkUndo);
+#endif  // !defined(OS_IOS)
+  if (register_bookmark_undo_service_as_observer) {
     bookmark_client->model()->AddObserver(
         BookmarkUndoServiceFactory::GetForProfile(profile));
   }
 #endif  // !defined(OS_ANDROID)
   return bookmark_client;
 }
 
 void BookmarkModelFactory::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   // Don't sync this, as otherwise, due to a limitation in sync, it
   // will cause a deadlock (see http://crbug.com/97955).  If we truly
   // want to sync the expanded state of folders, it should be part of
   // bookmark sync itself (i.e., a property of the sync folder nodes).
   registry->RegisterListPref(prefs::kBookmarkEditorExpandedNodes,
                              new base::ListValue,
                              user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 content::BrowserContext* BookmarkModelFactory::GetBrowserContextToUse(
     content::BrowserContext* context) const {
   return chrome::GetBrowserContextRedirectedInIncognito(context);
 }
 
 bool BookmarkModelFactory::ServiceIsNULLWhileTesting() const {
   return true;
 }