1) The current behavior feels contrary to the documentation; which says
"If true, will cause rebase-update to skip all processing on the branch."

2) The new behavior allows a workflow where 'master' is empty and
marked dormant, but kept up to date as the parent for all other
branches.

Change-Id: Ic7440706a69753f796846dd84ecbf8bcf172ba4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2128675
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>