[ObjC ARC] Converts ios/chrome/browser/web:test_support to ARC.

ios/chrome/browser/web/chrome_web_test.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.
 
 #import "ios/chrome/browser/web/chrome_web_test.h"
 
 #include "components/password_manager/core/browser/mock_password_store.h"
 #include "components/password_manager/core/browser/password_manager_test_utils.h"
 #include "ios/chrome/browser/browser_state/test_chrome_browser_state.h"
 #include "ios/chrome/browser/passwords/ios_chrome_password_store_factory.h"
 #import "ios/chrome/browser/ui/fullscreen_controller.h"
 #import "ios/web/public/web_state/web_state.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 ChromeWebTest::~ChromeWebTest() {}
 
 ChromeWebTest::ChromeWebTest() : web::WebTestWithWebState() {
   TestChromeBrowserState::Builder browser_state_builder;
   chrome_browser_state_ = browser_state_builder.Build();
 }
 
 void ChromeWebTest::SetUp() {
   web::WebTestWithWebState::SetUp();
   IOSChromePasswordStoreFactory::GetInstance()->SetTestingFactory(
       chrome_browser_state_.get(),
       &password_manager::BuildPasswordStore<
           web::BrowserState, password_manager::MockPasswordStore>);
   [FullScreenController setEnabledForTests:NO];
 }
 
 void ChromeWebTest::TearDown() {
   WaitForBackgroundTasks();
   [FullScreenController setEnabledForTests:YES];
   web::WebTestWithWebState::TearDown();
 }
 
 web::BrowserState* ChromeWebTest::GetBrowserState() {
   return chrome_browser_state_.get();
 }