Call decode() and encode() appropriately to manipulate bytes and strings.

Bug: 984182, 1009819
Change-Id: I8a73788ab912d6c6682012308954e4ab4df5fa98
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1859998
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>