Convert //services/js/echo_apptest.cc to use SynchronousInterfacePtr.

services/js/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("//mojo/public/mojo_application.gni")
 import("//testing/test.gni")
 
 group("js") {
   deps = [
     ":js_content_handler",
@@ skipping 59 matching lines @@
     "network_apptest.cc",
     "pingpong_apptest.cc",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/application",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/system",
     "//services/js/test:echo_service",
+    "//services/js/test:echo_service_sync",
     "//services/js/test:js_application_test_base",
     "//services/js/test:network_test_service",
     "//services/js/test:pingpong_service",
   ]
 }