left to right grouping

Bug: 905740
Change-Id: I6a0b971556ab66bec841004fbbe8760b9136f216
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1793775Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Anthony Polito <apolito@google.com>