sync: Gracefully handle very early shutdown

sync/internal_api/public/internal_components_factory.h

Index: sync/internal_api/public/internal_components_factory.h
diff --git a/sync/internal_api/public/internal_components_factory.h b/sync/internal_api/public/internal_components_factory.h
index 86509ec1d17d927f4153b389cbb48d3cd4b60dcb..606d5a4d8e30547ec6ec989dadc8a83d61a67cb1 100644
--- a/sync/internal_api/public/internal_components_factory.h
+++ b/sync/internal_api/public/internal_components_factory.h
@@ -21,6 +21,7 @@ namespace syncer {
 class ExtensionsActivity;
 class ServerConnectionManager;
 class SyncEngineEventListener;
+class CancellationSignal;
 class SyncScheduler;
 class TrafficRecorder;
 
@@ -75,7 +76,8 @@ class SYNC_EXPORT InternalComponentsFactory {
 
   virtual scoped_ptr<SyncScheduler> BuildScheduler(
       const std::string& name,
-      sessions::SyncSessionContext* context) = 0;
+      sessions::SyncSessionContext* context,
+      CancellationSignal* cancellation_signal) = 0;
 
   virtual scoped_ptr<sessions::SyncSessionContext> BuildContext(
       ServerConnectionManager* connection_manager,