This avoids the need to do the decoding everywhere separately.
Also a small fix for filter() no longer returning a list on Py3.

The scripts still work with Python 2.
There are no intended behaviour changes.

Bug: 942522
Change-Id: Id0f5153011b2ef1b64394359087864cd9434e45e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1595685
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Auto-Submit: Raul Tambre <raul@tambre.ee>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>