sync: Expose sync functionality as functions

sync/engine/sync_scheduler_impl.h

Index: sync/engine/sync_scheduler_impl.h
diff --git a/sync/engine/sync_scheduler_impl.h b/sync/engine/sync_scheduler_impl.h
index 3350267309179071b1e3b76e9e61d10603643e4a..342cb275f26dc75dea69b73c78850c2676f7abc2 100644
--- a/sync/engine/sync_scheduler_impl.h
+++ b/sync/engine/sync_scheduler_impl.h
@@ -130,6 +130,8 @@ class SYNC_EXPORT_PRIVATE SyncSchedulerImpl
                            ServerConnectionChangeDuringBackoff);
   FRIEND_TEST_ALL_PREFIXES(SyncSchedulerTest,
                            ConnectionChangeCanaryPreemptedByNudge);
+  FRIEND_TEST_ALL_PREFIXES(BackoffTriggersSyncSchedulerTest,
+                           FailGetEncryptionKey);
 
   struct SYNC_EXPORT_PRIVATE WaitInterval {
     enum Mode {
@@ -225,6 +227,9 @@ class SYNC_EXPORT_PRIVATE SyncSchedulerImpl
   // Creates a session for a poll and performs the sync.
   void PollTimerCallback();
 
+  // Returns the set of types that are enabled and not currently throttled.
+  ModelTypeSet GetEnabledAndUnthrottledTypes();
+
   // Called as we are started to broadcast an initial session snapshot
   // containing data like initial_sync_ended.  Important when the client starts
   // up and does not need to perform an initial sync.