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Adds a browser test equivalent of the framework that's
been used in instrumentation tests for VR testing and
ports over a simple WebVR presentation test as a proof
of concept. Additional tests will be ported over in
follow-up CLs.

Bug: 780668
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Id944f524e65056c15308a377e5c1260ce73e44ae
Reviewed-on: https://chromium-review.googlesource.com/809804Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Bill Orr <billorr@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524306}