Add Chromium environment application test support.

mojo/public/cpp/application/BUILD.gn

 # Copyright 2014 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.
 
 # GYP version: mojo/public/mojo_public.gyp:mojo_application_base
 source_set("application") {
   sources = [
     "application_connection.h",
     "application_delegate.h",
     "application_impl.h",
@@ skipping 30 matching lines @@
   public_deps = [ ":application" ]
 
   deps = [
     "//mojo/public/cpp/environment:standalone",
     "//mojo/public/cpp/utility",
   ]
 }
 
 source_set("test_support") {
   testonly = true
+  sources = [
+    "application_test_base.h",
+    "lib/application_test_base.cc",
+  ]
+
   deps = [
     ":application",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/environment",
     "//mojo/public/cpp/system",
     "//testing/gtest",
   ]
+}
 
-  sources = [
-    "application_test_base.h",
-    "lib/application_test_base.cc",
-    "lib/application_test_main.cc",
-  ]
+source_set("test_support_standalone") {
+  testonly = true
+  sources = [ "lib/application_test_main.cc", ]
+  public_deps = [ ":test_support", ]
+  deps = [ "//mojo/public/cpp/environment:standalone", ]
 }