[CodeHealth] Migrate remainder of testing/ to Python3 compatible syntax

and Pylint2.7, and fix resulting errors.

Bug: 1262363
Change-Id: I09628427dd4caf9d873f3b489b897054430f8567
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3557490
Reviewed-by: Ben Pastene <[email protected]>
Commit-Queue: Joshua Hood <[email protected]>
Cr-Commit-Position: refs/heads/main@{#996200}
NOKEYCHECK=True
GitOrigin-RevId: 8defc6c6da91e4b7d7a686b7bb67658d9a5ebe55
2 files changed