Add GN closure compilation for chromeos login.

This CL modifies the chromeos login closure compilation to use GN and
run on the main linux_chromium_rel_ng builder. The compilation can
be run locally by building the webui_closure_compile target.

Bug: 632206
TBR: [email protected]
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I9d61a132bcfaae43e62525a8a2b51a372b0f0d99
Reviewed-on: https://chromium-review.googlesource.com/706880
Commit-Queue: calamity <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#513667}
diff --git a/BUILD.gn b/BUILD.gn
index 66f617bc..cfcbd78 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1149,6 +1149,16 @@
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
+if (!is_win || !is_clang) {
+  group("webui_closure_compile") {
+    data_deps = []
+    if (is_chromeos) {
+      data_deps +=
+          [ "//chrome/browser/resources/chromeos/login:closure_compile" ]
+    }
+  }
+}
+
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }