headless: Add a headless shell

headless/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.
 
-source_set("launcher_support") {
-  sources = [
-    "chrome_launcher_support.cc",
-    "chrome_launcher_support.h",
+group("headless") {
+  deps = [
+    "//headless/lib:headless",
   ]
+}
+
+group("headless_shell") {
+  testonly = true
 
   deps = [
-    "//base",
+    "//headless/app:headless_shell",
   ]
 }