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This CL updates the uses of WebXR API in test pages.
Additionally, there is an update needed in webxr-version-shim.js.

Change-Id: If50624de7fed88c612751f709397755344e467c1
Reviewed-on: https://chromium-review.googlesource.com/c/1431915
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Bill Orr <billorr@chromium.org>
Auto-Submit: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625430}