Update Chomium's build files to work w/ latest GN binaries.

sandbox/linux/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 import("//testing/test.gni")
 
 declare_args() {
   compile_suid_client = is_linux
 
   compile_credentials = is_linux
 
   compile_seccomp_bpf_demo =
-      is_linux && (cpu_arch == "x86" || cpu_arch == "x64")
+      is_linux && (current_cpu == "x86" || current_cpu == "x64")
 }
 
 # We have two principal targets: sandbox and sandbox_linux_unittests
 # All other targets are listed as dependencies.
 # There is one notable exception: for historical reasons, chrome_sandbox is
 # the setuid sandbox and is its own target.
 
 group("sandbox") {
   deps = [
     ":sandbox_services",
@@ skipping 327 matching lines @@
   #      'type': 'none',
   #      'variables': {
   #        'test_suite_name': 'sandbox_linux_jni_unittests',
   #      },
   #      'dependencies': [
   #        'sandbox_linux_jni_unittests',
   #      ],
   #      'includes': [ '../../build/apk_test.gypi' ],
   #      }
 }