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

mandoline/services/updater/updater_impl.cc

Index: mandoline/services/updater/updater_impl.cc
diff --git a/mandoline/services/updater/updater_impl.cc b/mandoline/services/updater/updater_impl.cc
index bc0c05387744a565ed08834d49aad94f58492908..478722b7b73e1a9a86db529a954c9ea48fc12a9d 100644
--- a/mandoline/services/updater/updater_impl.cc
+++ b/mandoline/services/updater/updater_impl.cc
@@ -14,11 +14,9 @@
 
 namespace updater {
 
-UpdaterImpl::UpdaterImpl(mojo::ApplicationImpl* app_impl,
-                         UpdaterApp* application,
+UpdaterImpl::UpdaterImpl(UpdaterApp* application,
                          mojo::InterfaceRequest<Updater> request)
     : application_(application),
-      app_impl_(app_impl),
       binding_(this, std::move(request)) {}
 
 UpdaterImpl::~UpdaterImpl() {