GitLab

As per this spec:
https://wicg.github.io/reporting/#dictdef-reportingobserveroptions

Bug: 731810
Change-Id: I50840a97c2858fd04f397fd9799156d8e1e873c5
Reviewed-on: https://chromium-review.googlesource.com/1101312
Commit-Queue: Paul Meyer <paulmeyer@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568274}