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`wpt lint --ignore-glob` uses fnmatch to match patterns, which means
1. Patterns must match the full filename (we need a wildcard at the
   beginning).
2. Path separators are not treated specially (i.e. we need to use
   platform-dependent path separators).

Furthermore, we need to ignore OWNERS files, too, which was forgotten in
an earlier change.

Add tests to prevent regressions.

Fixed: 1103374
Change-Id: I62e6ea5ebef900c60b10a325f01683fa5ed836c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2326110
Commit-Queue: Robert Ma <robertma@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Auto-Submit: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792792}