[ObjC ARC] Converts ios/public/provider/chrome/browser/ui:ui to ARC.

ios/public/provider/chrome/browser/ui/default_ios_web_view_factory.mm

 // Copyright 2012 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/public/provider/chrome/browser/ui/default_ios_web_view_factory.h"
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 Class g_registered_factory_class = nil;
 }  // namespace
 
 @implementation DefaultIOSWebViewFactory
 
 + (void)registerWebViewFactory:(Class)webViewFactoryClass {
   DCHECK([webViewFactoryClass conformsToProtocol:@protocol(IOSWebViewFactory)]);
   g_registered_factory_class = webViewFactoryClass;
 }
 
 #pragma mark -
 #pragma mark IOSWebViewFactory
 
 + (UIWebView*)
     newExternalWebView:(IOSWebViewFactoryExternalService)externalService {
   if (g_registered_factory_class)
     return [g_registered_factory_class newExternalWebView:externalService];
   return [[UIWebView alloc] init];
 }
 
 @end