Revert of Service Manager: Remove ServiceContext* arg from Service::OnStart()

mash/session/session.h

Index: mash/session/session.h
diff --git a/mash/session/session.h b/mash/session/session.h
index 576492b102c1668fe2e33a710e3e8665b6c6e348..211387332757bece569bbe2760bf24ce3a8da958 100644
--- a/mash/session/session.h
+++ b/mash/session/session.h
@@ -18,6 +18,7 @@
 
 namespace service_manager {
 class Connection;
+class ServiceContext;
 }
 
 namespace mash {
@@ -32,7 +33,7 @@
 
  private:
   // service_manager::Service:
-  void OnStart() override;
+  void OnStart(service_manager::ServiceContext* context) override;
   bool OnConnect(const service_manager::ServiceInfo& remote_info,
                  service_manager::InterfaceRegistry* registry) override;
 
@@ -59,6 +60,8 @@
   void StartRestartableService(const std::string& url,
                                const base::Closure& restart_callback);
 
+  service_manager::ServiceContext* context_ = nullptr;
+
   std::map<std::string, std::unique_ptr<service_manager::Connection>>
       connections_;
   bool screen_locked_;