Prepare for moving nacl_irt_icache definition to the NaCl repository.

ppapi/nacl_irt/public/irt_nonsfi.h

 /*
  * Copyright 2014 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.
  */
+// TODO(mazda): Remove this file once NaCl has been rolled to the revision
+// that includes the definition of nacl_irt_icache.
+// https://code.google.com/p/nativeclient/issues/detail?id=4033
 
 #ifndef PPAPI_NACL_IRT_PUBLIC_IRT_NONSFI_H_
 #define PPAPI_NACL_IRT_PUBLIC_IRT_NONSFI_H_
 
+#if !defined(NACL_IRT_ICACHE_v0_1)
+
 #include <stddef.h>
 
 /*
  * This interface is only available on ARM, only for Non-SFI.
  */
 #define NACL_IRT_ICACHE_v0_1 "nacl-irt-icache-0.1"
 struct nacl_irt_icache {
   /*
    * clear_cache() makes instruction cache and data cache for the address
    * range from |addr| to |(intptr_t)addr + size| (exclusive) coherent.
    */
   int (*clear_cache)(void* addr, size_t size);
 };
 
+#endif
+
 #endif  // PPAPI_NACL_IRT_PUBLIC_IRT_NONSFI_H_