[ObjC ARC] Converts ios/web/public/test/fakes:fakes to ARC.

ios/web/public/test/fakes/test_navigation_manager.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.
 
 #import "ios/web/public/test/fakes/test_navigation_manager.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 TestNavigationManager::TestNavigationManager()
     : items_index_(-1),
       pending_item_(nullptr),
       last_committed_item_(nullptr),
       visible_item_(nullptr) {}
 
 TestNavigationManager::~TestNavigationManager() {}
 
@@ skipping 147 matching lines @@
 // navigation manager.
 void TestNavigationManager::AddItem(const GURL& url,
                                     ui::PageTransition transition) {
   items_.push_back(web::NavigationItem::Create());
   items_.back()->SetTransitionType(transition);
   items_.back()->SetURL(url);
   SetLastCommittedItemIndex(GetItemCount() - 1);
 }
 
 }  // namespace web