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

ash/mus/window_manager_application.h

Index: ash/mus/window_manager_application.h
diff --git a/ash/mus/window_manager_application.h b/ash/mus/window_manager_application.h
index 57c376eaec88cc0524e88f669920d2fd2997c6e2..9a9cf51c4fdce166290324d6da770a7085efa45d 100644
--- a/ash/mus/window_manager_application.h
+++ b/ash/mus/window_manager_application.h
@@ -27,6 +27,10 @@
 namespace system {
 class ScopedFakeStatisticsProvider;
 }
+}
+
+namespace service_manager {
+class ServiceContext;
 }
 
 namespace views {
@@ -72,12 +76,14 @@
   void ShutdownComponents();
 
   // 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;
 
   // session::mojom::ScreenlockStateListener:
   void ScreenlockStateChanged(bool locked) override;
+
+  service_manager::ServiceContext* context_ = nullptr;
 
   tracing::Provider tracing_;