Pepper: Move GetSandboxISA() to PPB_NaCl_Private.

components/nacl/renderer/arch_arm/sandbox_isa.cc

 // 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.
 
-#include "ppapi/native_client/src/trusted/plugin/nexe_arch.h"
-
 namespace {
 // The list of supported ISA strings for ARM.  See issue:
 //   http://code.google.com/p/nativeclient/issues/detail?id=1040 for more
 // information.  Note that these string are to be case-insensitive compared.
 const char* const kNexeArchARM = "arm";
 }  // namespace
 
-namespace plugin {
+namespace nacl {
 const char* GetSandboxISA() {
   return kNexeArchARM;
 }
-}  // namespace plugin
+}  // namespace nacl