[sync] Set up notification-free infra for triggering local sync refresh

components/sync_driver/sync_service.h

Index: components/sync_driver/sync_service.h
diff --git a/components/sync_driver/sync_service.h b/components/sync_driver/sync_service.h
index bdb75233691d4bdb60768bb9c120eadca813020d..d7ba6e55b0056222085f090df2cbb589216ba210 100644
--- a/components/sync_driver/sync_service.h
+++ b/components/sync_driver/sync_service.h
@@ -103,6 +103,10 @@ class SyncService : public DataTypeEncryptionHandler {
   // false.
   virtual bool IsSyncActive() const = 0;
 
+  // Triggers a GetUpdates call for the specified |types|, pulling any new data
+  // from the sync server.
+  virtual void TriggerRefresh(const syncer::ModelTypeSet& types) = 0;
+
   // Get the set of current active data types (those chosen or configured by
   // the user which have not also encountered a runtime error).
   // Note that if the Sync engine is in the middle of a configuration, this