`webkit-patch rebaseline{-cl}` likely does not support rebaselining flag-specific baselines very well. (Though I'm not sure how well it current works, as I've never tried it myself.)

This potentially blocks wpt-import in the following scenario:

1. Some tests that are already listed in some FlagExpectations are renamed in upstream.
2. Upon importing the rename, wpt-update-expectations automatically updates the corresponding lines in those FlagExpectations.
3. Changes in FlagExpectations trigger some additional bots in the CQ via WebKit/PRESUBMIT.py https://cs.chromium.org/chromium/src/third_party/WebKit/PRESUBMIT.py?q=third_party/WebKit/PRESUBMIT&sq=package:chromium&l=222
4. If some other changes in the import cause the additional bots to fail, the import will fail to pass CQ.

Automatic rebaseline will also ease some maintenance burden of LayoutNG and alike. IIUC, currently owners of these flags have to do manual rebaseline (or with some ad-hoc cron jobs) every so often, and I expect WPT to be the fastest moving piece.

It's not clear to me how big the scope of this task is. And I've only seen one case blocking the import in the past 6 months. Hence I'm filing as P3, but we can surely discuss and re-prioritize.