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There were a number of issues with lifetime that would cause issues,
such as multiple initializations of OpenVR, multiple conflicting
OpenVRDevices, and leaking objects.

This change fixes those so OpenVRDeviceProvider owns OpenVRDevice, which
owns OpenVRRenderLoop, and OpenVRRenderLoop correctly cleans up its bindings.

Change-Id: I32ee8abaa70a8a13155448e697d318c675f1d9ed
Reviewed-on: https://chromium-review.googlesource.com/777787Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517649}