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Previously, we create a GvrDevice even if VrShellDelegate thinks VR is not
available. This GvrDevice may works for magic window but can't present as Vr
presentation depend on VrShellDelegate. However, the returned GvrDevice marks
itself as a device which set canPresent to true. This leads to confusion.

This CL gate GvrDevice creation on the same criteria as VrShellDelegate.

Bug: 790770
Change-Id: I686eda152418b71ad5c5344aed593903db2b70f7
Reviewed-on: https://chromium-review.googlesource.com/809227Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: Biao She <bshe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522182}