Add scripts to support running WPT on Chromium CI.

testing/scripts/run_wpt_tests.py is used to adapt swarming flags to WPT
flags (eg: for sharding), and also to kick-off the update_wpt_output.py
cleanup step.

t_p/b/t/build_wpt_metadata.py is for converting
Chromium TestExpectations files into WPT Metadata files for skipped
tests.

t_p/b/t/update_wpt_output.py is run as a cleanup step on
each shard. It rewrites the output of a WPT run by inserting expected
statuses from the TestExpectations file, which includes supporting flaky
tests (ie: multiple expected statuses) which WPT doesn't currently
understand.

Bug: 937369
Change-Id: Ic7d2c037ec545f38a1101759db6eb04db54057c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660702
Commit-Queue: Luke Z <lpz@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672059}
7 files changed