unpack-trees: add trace2 regions

The unpack_trees() method is quite complicated and its performance can
change dramatically depending on how it is used. We already have some
performance tracing regions, but they have not been updated to the
trace2 API. Do so now.

We already have trace2 regions in unpack_trees.c:clear_ce_flags(), which
uses a linear scan through the index without recursing into trees.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

unpack-trees.c

@@ -1580,6 +1580,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
 
 	trace_performance_enter();
+	trace2_region_enter("unpack_trees", "unpack_trees", the_repository);
+
 	if (!core_apply_sparse_checkout || !o->update)
 		o->skip_sparse_checkout = 1;
 	if (!o->skip_sparse_checkout && !o->pl) {
@@ -1653,7 +1655,9 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		}
 
 		trace_performance_enter();
+		trace2_region_enter("unpack_trees", "traverse_trees", the_repository);
 		ret = traverse_trees(o->src_index, len, t, &info);
+		trace2_region_leave("unpack_trees", "traverse_trees", the_repository);
 		trace_performance_leave("traverse_trees");
 		if (ret < 0)
 			goto return_failed;
@@ -1741,6 +1745,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 done:
 	if (free_pattern_list)
 		clear_pattern_list(&pl);
+	trace2_region_leave("unpack_trees", "unpack_trees", the_repository);
 	trace_performance_leave("unpack_trees");
 	return ret;