Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

mojo/shell/public/cpp/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/mojo_base.gyp:mojo_application_base
 source_set("cpp") {
   public_deps = [
     ":init_commandline",
     ":sources",
   ]
@@ skipping 23 matching lines @@
     "lib/application_impl.cc",
     "lib/application_runner.cc",
     "lib/interface_factory_connector.h",
     "lib/service_connector_registry.cc",
     "lib/service_connector_registry.h",
     "lib/service_provider_impl.cc",
     "lib/service_registry.cc",
     "lib/service_registry.h",
     "service_connector.h",
     "service_provider_impl.h",
+    "shell.h",
   ]
 
   deps = [
     "//base:i18n",
     "//mojo/common",
     "//mojo/converters/network",
     "//mojo/environment:chromium",
     "//mojo/message_pump",
   ]
 
@@ skipping 48 matching lines @@
     "//mojo/public/cpp/environment",
     "//mojo/public/cpp/system",
     "//mojo/shell/public/interfaces:interfaces_cpp_sources",
   ]
 
   data_deps = []
   if (is_android) {
     data_deps += [ "//mojo/android" ]
   }
 }