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This removes WMR's support for WebVR, and refactors some helpers that
existed to simplify those code paths.

Also fixes a few lint errors for these files.

Fixed: 1017847
Change-Id: I95d60fe4892f37febbda0a383e2bf270441f2845
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879661Reviewed-by: Jacob DeWitt <jacde@chromium.org>
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709692}