[ObjC ARC] Converts ios/chrome/test/base:base to ARC.

ios/chrome/test/base/scoped_block_swizzler.mm

 // Copyright 2013 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.
 
 #include "ios/chrome/test/base/scoped_block_swizzler.h"
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 ScopedBlockSwizzler::ScopedBlockSwizzler(Class target, SEL selector, id block) {
   method_ = class_getInstanceMethod(target, selector);
   if (!method_) {
     // Try swizzling a class method instead.
     method_ = class_getClassMethod(target, selector);
   }
   DCHECK(method_);
 
   IMP block_imp = imp_implementationWithBlock(block);
   original_imp_ = method_setImplementation(method_, block_imp);
 }
 
 ScopedBlockSwizzler::~ScopedBlockSwizzler() {
   IMP block_imp = method_setImplementation(method_, original_imp_);
   DCHECK(imp_removeBlock(block_imp));
 }