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

ios/web/public/test/crw_mock_web_state_delegate.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/crw_mock_web_state_delegate.h"
 
 #import "ios/web/public/web_state/context_menu_params.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
+
 @implementation CRWMockWebStateDelegate {
   // Backs up the property with the same name.
   std::unique_ptr<web::WebState::OpenURLParams> _openURLParams;
   // Backs up the property with the same name.
   std::unique_ptr<web::ContextMenuParams> _contextMenuParams;
   // Backs up the property with the same name.
   BOOL _javaScriptDialogPresenterRequested;
 }
 
 @synthesize webState = _webState;
@@ skipping 58 matching lines @@
 
 - (web::ContextMenuParams*)contextMenuParams {
   return _contextMenuParams.get();
 }
 
 - (BOOL)javaScriptDialogPresenterRequested {
   return _javaScriptDialogPresenterRequested;
 }
 
 @end