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Many tests of CSS.registerProperty were written, but none have been
upstreamed to WPT. Upstream these tests to ensure interoperability.

Bug: 641877
Change-Id: I8272b14c78cb75bb6f5f3cedb770091cbcba522a
Reviewed-on: https://chromium-review.googlesource.com/959422Reviewed-by: Robert Ma <robertma@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Chris Nardi <cnardi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542649}