[ObjC ARC] Converts ios/web:ios_web_navigation_unittests to ARC.

ios/web/navigation/navigation_item_storage_test_util.mm

 // Copyright 2017 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.
 
 #import "ios/web/navigation/navigation_item_storage_test_util.h"
 
 #import "ios/web/public/crw_navigation_item_storage.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 BOOL ItemStoragesAreEqual(CRWNavigationItemStorage* item1,
                           CRWNavigationItemStorage* item2) {
   return item1.virtualURL == item2.virtualURL &&
          item1.referrer.url == item2.referrer.url &&
          item1.referrer.policy == item2.referrer.policy &&
          item1.timestamp == item2.timestamp && item1.title == item2.title &&
          item1.displayState == item2.displayState &&
          item1.shouldSkipRepostFormConfirmation ==
              item2.shouldSkipRepostFormConfirmation &&
          item1.userAgentType == item2.userAgentType &&
          [item1.POSTData isEqualToData:item2.POSTData] &&
          [item1.HTTPRequestHeaders
              isEqualToDictionary:item2.HTTPRequestHeaders];
 }
 
 }  // namespace web