Land prep work to enable NaCl in the Linux x64 GN builds.

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

Index: ppapi/native_client/src/untrusted/irt_stub/BUILD.gn
diff --git a/ppapi/native_client/src/untrusted/irt_stub/BUILD.gn b/ppapi/native_client/src/untrusted/irt_stub/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..fd781870a7337ccff9a84bc7ef9a96f3b6eb4586
--- /dev/null
+++ b/ppapi/native_client/src/untrusted/irt_stub/BUILD.gn
@@ -0,0 +1,16 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.

[brettw, 2015/02/05 00:20:36]

2015

+# 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) {

[Nick Bray (chromium), 2015/02/05 23:21:46]

Nit: technically not needed?  If we're including _any_ file in the untrusted
directory without enable_nacl_untrusted being true, something is seriously
wrong.  I wouldn't mind leaving this in as a sanity check, however, if you
comment it.

[Dirk Pranke, 2015/02/05 23:52:19]

This is probably better changed to an assert() then. Will do so.

[Nick Bray (chromium), 2015/02/06 01:18:00]

asserting is_nacl would be the cleanest approach, I think.

+  static_library("ppapi_stub_lib") {
+    sources = [
+      "ppapi_plugin_main.c",
+      "ppapi_plugin_start.c",
+      "plugin_main_irt.c",
+      "thread_creator.c",
+    ]
+  }
+}