Add a sandbox API for broker handle duplication

sandbox/src/ipc_tags.h

Index: sandbox/src/ipc_tags.h
===================================================================
--- sandbox/src/ipc_tags.h	(revision 128951)
+++ sandbox/src/ipc_tags.h	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -28,6 +28,7 @@
   IPC_OPENEVENT_TAG,
   IPC_NTCREATEKEY_TAG,
   IPC_NTOPENKEY_TAG,
+  IPC_DUPLICATEHANDLEPROXY_TAG,
   IPC_LAST_TAG
 };