Add a ClientAction used by SyncRollbackManager to notify PSS that rollback is

sync/protocol/sync_protocol_error.h

Index: sync/protocol/sync_protocol_error.h
diff --git a/sync/protocol/sync_protocol_error.h b/sync/protocol/sync_protocol_error.h
index aef76501e7c85ed1e86cb8cb27e373e07ec4ce0e..0c825b76475644b7e3c054a9b0560b467bb520dd 100644
--- a/sync/protocol/sync_protocol_error.h
+++ b/sync/protocol/sync_protocol_error.h
@@ -72,6 +72,10 @@ enum ClientAction {
   // Disable sync and roll back local model to pre-sync state.
   DISABLE_SYNC_AND_ROLLBACK,
 
+  // Generated by SyncRollbackManager to notify ProfileSyncService that
+  // rollback is finished.
+  ROLLBACK_DONE,
+
   // The default. No action.
   UNKNOWN_ACTION
 };