P1 since it's blocking another P1.

Not captured in the description is translating a GitHub @username to someone@chromium.org.

For example, I wouldn't mind seeing reviews in external/wpt/fullscreen, where I am in the upstream OWNERS file, and I'm not sure if it's possible to subscribe to components in reviews?

Since we currently don't sync OWNERS anyway, I think adding a sync for individual OWNERS is a separate problem. It is also non-trivial since one would need to keep a mapping somewhere and make sure that it stays up-to-date with actual owners.

Therefore, I think this should not be implemented as part of this bug. If in the future we will decide to add support for individual OWNERS, we can then replace the presubmit check mentioned in the description with the one that will check the mapping before adding owners.

Keeping the OWNERS files completely separate (no mapping between them) for now SGTM.  Note that the upstream files have an entirely different semantic from our notion of "OWNERS" - they're really a WATCHLIST file: https://github.com/w3c/web-platform-tests/blob/master/README.md#test-review.

CL: https://codereview.chromium.org/2779053002

So what's the resolution here? We have OWNERS files in the chromium repo that only contain teams/bug components and that we don't sync upstream? If so, that SGTM.

Yes, that's the resolution and the above CL will implement this. OWNERS files are NOT synchronized both ways.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/54b5563663f325d159f01efa846e74c803c65119

commit 54b5563663f325d159f01efa846e74c803c65119
Author: sergiyb <sergiyb@chromium.org>
Date: Tue Mar 28 19:38:45 2017

Ignore OWNERS files during external/wpt import and export

R=qyearsley@chromium.org
BUG= 702283 

Review-Url: https://codereview.chromium.org/2779053002
Cr-Commit-Position: refs/heads/master@{#460190}

[modify] https://crrev.com/54b5563663f325d159f01efa846e74c803c65119/third_party/WebKit/Tools/Scripts/webkitpy/w3c/chromium_commit.py
[modify] https://crrev.com/54b5563663f325d159f01efa846e74c803c65119/third_party/WebKit/Tools/Scripts/webkitpy/w3c/chromium_commit_unittest.py
[modify] https://crrev.com/54b5563663f325d159f01efa846e74c803c65119/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py
[modify] https://crrev.com/54b5563663f325d159f01efa846e74c803c65119/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer_unittest.py

CL has landed, but where is this service running? Do I need to deploy changes to it manually or will it update itself?

The service consists of a couple builders running recipes on the chromium.infra.cron master:

 Import: https://build.chromium.org/p/chromium.infra.cron/builders/w3c-test-autoroller
 Export: https://build.chromium.org/p/chromium.infra.cron/builders/wpt-exporter

Currently, the import only happens once per day, and today is a special day since the csswg-test repo just got merged into web-platform-tests; export script is run continuously.

No need to deploy changes manually; since the recipes run scripts in chromium/src, and so the next time it starts the changes should be in effect :-)

This means we should be able to start adding OWNERS files into subdirectories of LayoutTests/external/wpt/, and neither the importer or exporter should touch  the new files.

Thanks for explaining. I've landed hundreds of OWNERS files here: http://crrev.com/2751113002 and looks like they are not exported, e.g. compare https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/LayoutTests/external/wpt/FileAPI/OWNERS and https://github.com/w3c/web-platform-tests/blob/master/FileAPI/OWNERS.