[iOS/OS X] Allow base::scoped_nsobject<> to be used when ARC is enabled.

base/mac/scoped_block.h

 // Copyright (c) 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.
 
 #ifndef BASE_MAC_SCOPED_BLOCK_H_
 #define BASE_MAC_SCOPED_BLOCK_H_
 
 #include <Block.h>
 
 #include "base/mac/scoped_typeref.h"
 
 namespace base {
 namespace mac {
 
 namespace internal {
 
+id ScopedBlockTraitsRetain(id block);

[Mark Mentovai, 2016/04/05 00:09:15]

Blocks are normally typed as const void*. If you use that, does it break ARC?
That would be worth a comment, because the type mismatch compared to <Block.h>
is obvious.

Does this file need to be #included by any non-Objective C++ files?

+void ScopedBlockTraitsRelease(id block);
+
 template <typename B>
 struct ScopedBlockTraits {
   static B InvalidValue() { return nullptr; }
-  static B Retain(B block) { return Block_copy(block); }
-  static void Release(B block) { Block_release(block); }
+  static B Retain(B block) { return ScopedBlockTraitsRetain(block); }
+  static void Release(B block) { ScopedBlockTraitsRelease(block); }
 };
 
 }  // namespace internal
 
 // ScopedBlock<> is patterned after ScopedCFTypeRef<>, but uses Block_copy() and
 // Block_release() instead of CFRetain() and CFRelease().
 
 template <typename B>
 using ScopedBlock = ScopedTypeRef<B, internal::ScopedBlockTraits<B>>;
 
 }  // namespace mac
 }  // namespace base
 
 #endif  // BASE_MAC_SCOPED_BLOCK_H_