Improve PPAPI scripts' Python 3 support

This mostly includes low-hanging fruit.

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

Bug: 941669
Change-Id: Ie950398b967b749f8136b4aea19592b6b50083ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1556774
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Auto-Submit: Raul Tambre <raul@tambre.ee>
Cr-Original-Commit-Position: refs/heads/master@{#648792}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a4895d8a40bb7d8566d0c2df81a54a5e35bfb295
21 files changed