Add a TODO to seek in FindCommonAncestor implementation.

go/store/datas/commit.go

@@ -193,6 +193,7 @@ func FindCommonAncestor(ctx context.Context, c1, c2 types.Ref, vr1, vr2 types.Va
 			return r, true, nil
 		}
 		if pi1.Less(vr1.Format(), pi2) {
+			// TODO: Should pi2.Seek(pi1.curr), but MapIterator does not expose Seek yet.
 			if !pi2.Next(ctx) {
 				return types.Ref{}, false, firstError(pi1.Err(), pi2.Err())
 			}