From https://chromium-review.googlesource.com/c/chromium/src/+/1413502/#message-f36f8261192e3317d91994650e6d8edfaf52ef61 (thanks domenic@):

- List filenames in BUILD.gn (e.g. resources/layered_api/*/BUILD.gn),
- A script then automatically generates the .grdp and .h file as part of the build.

Benefits:

- OWNERS are aligned with the built-in files themselves (resources/layered_api/*/OWNERS).
- More aligned with how adding C++ files work.

Probably this should be done together with other LAPI development mechanics improvements, because how the built-in files are managed/developed (e.g. moving them to github-first) will affect this issue.

Assigning to myself for tracking.