[ObjC ARC] Converts ios/chrome/test/app:test_support to ARC.

ios/chrome/test/app/bookmarks_test_util.mm

 // Copyright 2016 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 "ios/chrome/test/app/bookmarks_test_util.h"
 
 #include "components/bookmarks/browser/bookmark_model.h"
 #include "ios/chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "ios/chrome/browser/bookmarks/bookmarks_utils.h"
 #import "ios/chrome/test/app/chrome_test_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace chrome_test_util {
 
 bool BookmarksLoaded() {
   bookmarks::BookmarkModel* bookmarkModel =
       ios::BookmarkModelFactory::GetForBrowserState(GetOriginalBrowserState());
   return bookmarkModel->loaded();
 }
 
 bool ClearBookmarks() {
   ios::ChromeBrowserState* browserState = GetOriginalBrowserState();
   bookmarks::BookmarkModel* bookmarkModel =
       ios::BookmarkModelFactory::GetForBrowserState(browserState);
   BOOL removeSucceeded = RemoveAllUserBookmarksIOS(browserState);
   return removeSucceeded && !bookmarkModel->HasBookmarks();
 }
 
 }  // namespace chrome_test_util