Replace ApplicationImpl::CreateApplicationConnector() with a standalone helper function.

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.
 
 import("../../mojo_sdk.gni")
 
 # GYP version: mojo/public/mojo_public.gyp:mojo_application_base
 mojo_sdk_source_set("application") {
   sources = [
     "application_delegate.h",
     "application_impl.h",
     "connect.h",
     "connection_context.h",
     "lib/application_delegate.cc",
     "lib/application_impl.cc",
+    "lib/connect.cc",
     "lib/service_provider_impl.cc",
     "service_connector.h",
     "service_provider_impl.h",
   ]
 
   mojo_sdk_deps = [
     "mojo/public/cpp/bindings",
     "mojo/public/cpp/environment",
     "mojo/public/cpp/system",
     "mojo/public/interfaces/application",
@@ skipping 51 matching lines @@
   ]
 
   mojo_sdk_deps = [
     "mojo/public/interfaces/application",
     "mojo/public/cpp/environment:standalone",
     "mojo/public/cpp/system",
     "mojo/public/cpp/utility",
     "mojo/public/interfaces/application",
   ]
 }