The `author` parameter is never set.
The `local_description` parameter was only set with the
purpose of getting the local description, so separate it into its
own method and call that instead.
Use the absolute root when getting the list of modified files instead.

Bug: 1042324
Change-Id: I8505172edaacee0656dda98ebbd5f8ebfacb3cef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2038050
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>