The patch extends the OutputHLSL and DynamicHLSL translators to
select the viewport index in the geometry shader and propagate
the ViewID variable to the fragment shader.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I9e344a7521e2e1137e6eb38d0bfecea8bece778f
Reviewed-on: https://chromium-review.googlesource.com/608967
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>