[vr] Handle SecurityException when querying VrCore version

Bug: 773256
Change-Id: I0991b5c525420384ec422d23ae7b9f6af35e7787
Reviewed-on: https://chromium-review.googlesource.com/782159


Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518293}