[Sync] Add SyncEncryptionHandler

sync/syncable/nigori_util.h

Index: sync/syncable/nigori_util.h
diff --git a/sync/syncable/nigori_util.h b/sync/syncable/nigori_util.h
index 2edc9cdff5df98cc2f76cdf40daec429d501a7bd..65c51dedb1533bd44722bbfa1dfb4fecbed39839 100644
--- a/sync/syncable/nigori_util.h
+++ b/sync/syncable/nigori_util.h
@@ -68,6 +68,12 @@ bool UpdateEntryWithEncryption(
     const sync_pb::EntitySpecifics& new_specifics,
     MutableEntry* entry);
 
+// Updates |nigori| to match the encryption state specified by |encrypted_types|
+// and |encrypt_everything|.
+void UpdateNigoriFromEncryptedTypes(ModelTypeSet encrypted_types,
+                                    bool encrypt_everything,
+                                    sync_pb::NigoriSpecifics* nigori);
+
 }  // namespace syncable
 }  // namespace syncer