[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"
 
+#if defined(__has_feature) && __has_feature(objc_arc)
+#define BASE_MAC_BRIDGE_CAST(TYPE, VALUE) (__bridge TYPE)(VALUE)
+#else
+#define BASE_MAC_BRIDGE_CAST(TYPE, VALUE) VALUE
+#endif
+
 namespace base {
 namespace mac {
 
 namespace internal {
 
 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 BASE_MAC_BRIDGE_CAST(
+        B, Block_copy(BASE_MAC_BRIDGE_CAST(const void*, block)));
+  }
+  static void Release(B block) {
+    Block_release(BASE_MAC_BRIDGE_CAST(const void*, 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
 
+#undef BASE_MAC_BRIDGE_CAST
+
 #endif  // BASE_MAC_SCOPED_BLOCK_H_