Dart: Adds a content handler and a test.

services/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.
 
 import("//build/config/ui.gni")
+import("//mojo/public/mojo.gni")
 
 group("services") {
   deps = [
     "//services/clipboard",
     "//services/fake_surfaces",
     "//services/gles2:lib",
     "//services/http_server",
     "//services/http_server/public",
     "//services/icu_data",
     "//services/js",
     "//services/native_viewport",
     "//services/surfaces",
     "//services/test_service:bindings",
     "//services/tracing",
     "//services/view_manager",
     "//services/window_manager",
   ]
+
+  if (mojo_use_dart) {
+    deps += [ "//services/dart" ]
+  }
 }