Build NaCl in the CrOS GN builds and make sure "all" works

ppapi/native_client/src/untrusted/pnacl_support_extension/BUILD.gn

 # Copyright 2015 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")
 
 if (enable_nacl && enable_nacl_untrusted && enable_pnacl) {
   # This target copies files from the prebuilt/DEPS'ed in pnacl_translator
   # toolchain and copies the latest PNaCl IRT shim library.
   # We could use 'copies', but we want to rename the files in a white-listed
@@ skipping 83 matching lines @@
       }
     } else {
       assert(false, "unhandled target_cpu")
     }
     args = [
       "--dest",
       rebase_path("$root_out_dir/pnacl", root_build_dir),
     ]
     args += shim_override_args
 
+    if (current_os == "chromeos") {
+      toolchain_os = "linux"
+    } else {
+      toolchain_os = current_os
+    }
+
     args += [
       "--target_arch",
       target_cpu,
       "--info_template_path",
       rebase_path("//native_client/pnacl/driver/pnacl_info_template.json",
                   root_build_dir),
       "--pnacl_translator_path",
       rebase_path(
-          "//native_client/toolchain/${current_os}_x86/pnacl_translator",
+          "//native_client/toolchain/${toolchain_os}_x86/pnacl_translator",
           root_build_dir),
       "--package_version_path",
       rebase_path("//native_client/build/package_version/package_version.py",
                   root_build_dir),
       "--pnacl_package_name",
       "pnacl_translator",
 
       # ABI Version Number
       "1",
     ]
   }
 }