This patch intends to add missing initialization of MAX_INTEGER_SAMPLES,
MAX_DEPTH_TEXTURE_SAMPLES and MAX_COLOR_TEXTURE_SAMPLES required for
multisampled textures on D3D backends.

Since MAX_*_SAMPLES cannot be queried directly from D3D APIs, these
values are initially assigned a large value in renderer11.cpp and
re-calculated in context::updateCaps().

This patch also adds tests to ensure these values are greater than 1
as required in OpenGL ES3.1 spec.

BUG=angleproject:1592
TEST=angle_end2end_tests

Change-Id: Iba586e311d40d2da4569816902f96e40bbd6935b
Reviewed-on: https://chromium-review.googlesource.com/597411
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>