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

ios/web/public/test/fakes/test_native_content_provider.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_native_content_provider.h"
 
 #include <map>
 
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation TestNativeContentProvider {
   std::map<GURL, id<CRWNativeContent>> _nativeContent;
 }
 
 - (void)setController:(id<CRWNativeContent>)controller forURL:(const GURL&)URL {
   _nativeContent[URL] = controller;
 }
 
 - (BOOL)hasControllerForURL:(const GURL&)URL {
   return _nativeContent.find(URL) != _nativeContent.end();
 }
 
 - (id<CRWNativeContent>)controllerForURL:(const GURL&)URL
                                 webState:(web::WebState*)webState {
   auto nativeContent = _nativeContent.find(URL);
   if (nativeContent == _nativeContent.end()) {
     return nil;
   }
   return nativeContent->second;
 }
 
 - (id<CRWNativeContent>)controllerForURL:(const GURL&)URL
                                withError:(NSError*)error
                                   isPost:(BOOL)isPost {
   NOTREACHED();
   return nil;
 }
 
 @end