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

base/mac/scoped_nsobject.mm

Index: base/mac/scoped_nsobject.mm
diff --git a/base/mac/scoped_nsobject.mm b/base/mac/scoped_nsobject.mm
new file mode 100644
index 0000000000000000000000000000000000000000..65b40317dc716338bc1341a6f38225dd58689ab1
--- /dev/null
+++ b/base/mac/scoped_nsobject.mm
@@ -0,0 +1,23 @@
+// Copyright 2016 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 "base/mac/scoped_nsobject.h"
+
+namespace base {
+namespace internal {
+
+id ScopedNSProtocolTraitsRetain(id obj) {
+  return [obj retain];
+}
+
+id ScopedNSProtocolTraitsAutoRelease(id obj) {
+  return [obj autorelease];
+}
+
+void ScopedNSProtocolTraitsRelease(id obj) {
+  return [obj release];
+}
+
+}  // namespace internal
+}  // namespace base