Because the ANGLE_multiview extension uses instancing to multiply
geometry for each view, Draw* calls with an active multiview program
have to be handled in the follwing way:
1) Convert non-instanced Draw calls to their instanced versions.
2) Multiply the number of instances in an instanced Draw call by the
number of views.
The patch also applies the viewport offsets to the viewport and scissor
rectangle and propagates the computed viewports and scissors to the
D3D11 runtime.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I8b4295c95c2cc0c1046c67e1fb1a782a46703292
Reviewed-on: https://chromium-review.googlesource.com/618331
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>