Fix shader support of OVR_multiview Fix up incorrect capitalization of gl_ViewID_OVR in a few places. Also add extension macro test to compiler unit tests. BUG=angleproject:1669 TEST=angle_unittests Change-Id: Ia7fdd747ad08355cdc149db9e2e7911c2e673af5 Reviewed-on: https://chromium-review.googlesource.com/425851 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>