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- This API can be used to exit VR when we encounter an unsupported
  feature.
- Make unhandled page info request use this API.

Change-Id: I974466cc40241f570aecb1ac08bb15b510bd57d2
Reviewed-on: https://chromium-review.googlesource.com/578209Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488454}