The patch enables the ANGLE_multiview extension in the D3D11 renderer
and determines the maximum number of available views.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I56e434a14c61df3d6ab66c2863ce783fcdcc5a93
Reviewed-on: https://chromium-review.googlesource.com/595507
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>