[ObjC ARC] Converts ios/chrome/browser/ui/bookmarks:unit_tests to ARC.

ios/chrome/browser/ui/bookmarks/bookmark_ios_unittest.mm

 // Copyright 2014 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/browser/ui/bookmarks/bookmark_ios_unittest.h"
 
 #include "base/message_loop/message_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/bookmarks/browser/bookmark_model.h"
 #include "components/bookmarks/test/bookmark_test_helpers.h"
 #include "ios/chrome/browser/bookmarks/bookmark_model_factory.h"
 #import "ios/chrome/browser/browser_state/test_chrome_browser_state.h"
 #include "ios/web/public/test/test_web_thread.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 using bookmarks::BookmarkNode;
 
 BookmarkIOSUnitTest::BookmarkIOSUnitTest() {}
 BookmarkIOSUnitTest::~BookmarkIOSUnitTest() {}
 
 void BookmarkIOSUnitTest::SetUp() {
   // Get a BookmarkModel from the test ChromeBrowserState.
   TestChromeBrowserState::Builder test_cbs_builder;
   chrome_browser_state_ = test_cbs_builder.Build();
   chrome_browser_state_->CreateBookmarkModel(true);
@@ skipping 14 matching lines @@
                                                    NSString* title) {
   base::string16 c_title = base::SysNSStringToUTF16(title);
   return _bookmarkModel->AddFolder(parent, parent->child_count(), c_title);
 }
 
 void BookmarkIOSUnitTest::ChangeTitle(NSString* title,
                                       const BookmarkNode* node) {
   base::string16 c_title = base::SysNSStringToUTF16(title);
   _bookmarkModel->SetTitle(node, c_title);
 }