The patch checks whether ANGLE_multiview can be supported in the OpenGL
renderer, updates the caps and adds a workaround field to enable
multiview support through the NV_viewport_array2 extension.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I99dae10564db7bcca41d7624f8de272c1d996e09
Reviewed-on: https://chromium-review.googlesource.com/567934Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>