Update from https://crrev.com/327068

sky/engine/bindings/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("//sky/engine/bindings/bindings.gni")
 import("//sky/engine/core/core.gni")
 
 source_set("bindings") {
   sources = [
     "builtin.cc",
@@ skipping 71 matching lines @@
     rebase_path("$gen_snapshot_dir/gen_snapshot"),
     "--package_root",
     rebase_path("$root_gen_dir"),
     "--script",
     rebase_path("snapshot.dart"),
     "--vm_output_bin",
     rebase_path(vm_isolate_snapshot, root_build_dir),
     "--output_bin",
     rebase_path(isolate_snapshot, root_build_dir),
     "--target_os",
-    os,
+    target_os,

[Nick Bray (chromium), 2015/05/05 23:27:23]

Yes, it's kinda freaky you would pass "current_os" to "--target_os", but...
yeah.

     "--url_mapping=dart:sky,$dart_sky_path",
     "--url_mapping=dart:mojo.internal,$internal_path",
     "--url_mapping=dart:sky_builtin,$builtin_path",
   ]
 }
 
 action("generate_snapshot_file") {
   deps = [
     ":generate_snapshot_bin",
   ]
@@ skipping 278 matching lines @@
   ]
 
   include_dirs = [
     "..",
     "$root_build_dir",
   ]
 
   sources = get_target_outputs(":compile_idls")
   sources += get_target_outputs(":generate_dart_globals")
 }