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

mojo/public/cpp/application/lib/connect.cc

+// Copyright 2016 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.
+
+#include "mojo/public/cpp/application/connect.h"
+
+#include "mojo/public/interfaces/application/shell.mojom.h"
+
+namespace mojo {
+
+InterfaceHandle<ApplicationConnector> CreateApplicationConnector(Shell* shell) {
+  InterfaceHandle<ApplicationConnector> application_connector;
+  shell->CreateApplicationConnector(GetProxy(&application_connector));
+  return application_connector;
+}
+
+}  // namespace mojo