This is a bug for the failures which happened over the  (which Rick was already looking at yesterday).

Example build: 

https://luci-milo.appspot.com/buildbot/chromium.infra.cron/wpt-importer/366

Log excerpt:

Import complete
Deleting any orphaned baselines.
Generating MANIFEST.json
Updating TestExpectations for any removed or renamed tests.
# ret> 1
Committing changes.
# ret> 1
# out> On branch update_wpt
# out> Your branch is ahead of 'origin/master' by 1 commit.
# out>   (use "git push" to publish your local commits)
# out> nothing to commit, working tree clean
step returned non-zero exit code: 1

I highly suspect that this is due to a bug I introduced in a recent commit.

Recent commits: https://chromium.googlesource.com/chromium/src/+log/d6a190b042fb9dfe980fae5e3a5d8ed62b7605fd/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py

It appears like `self._has_changes()` is returning true but `self.run(['git', 'commit', '--all', '-F', '-'], stdin=commit_message)` exits and says there is nothing to commit.

https://cs.chromium.org/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py?l=113

I'm able to reproduce this locally and will investigate today.