Add session metrics for WebXR on desktop

Bug: 912978
Change-Id: Ic64fd90848811541bb487fc235926af44dca5bc7
Reviewed-on: https://chromium-review.googlesource.com/c/1475072
Commit-Queue: Bill Orr <billorr@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634476}
1 file changed