Converts parts of ios/web to ARC

ios/web/alloc_with_zone_interceptor.mm

 // Copyright 2015 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/alloc_with_zone_interceptor.h"
 
 #import <objc/runtime.h>
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 void AddAllocWithZoneMethod(Class target, id (^impl_block)(Class, NSZone*)) {
   // Make sure |allocWithZone:| is not already implemented in the target class.
   Class meta_class = object_getClass(target);
   DCHECK_EQ(
       class_getMethodImplementation(meta_class, @selector(allocWithZone:)),
       class_getMethodImplementation(object_getClass([NSObject class]),
                                     @selector(allocWithZone:)));
 
   IMP new_impl = imp_implementationWithBlock(^(id self, NSZone* zone) {
     return impl_block(self, zone);
   });
   class_addMethod(meta_class, @selector(allocWithZone:), new_impl, "v@:@");
 }
 
 }  // namespace web