Saves us some time on startup. Also assume every multisample format
can support 1x multisampling, and that if we support a higher format
we support all lower sample counts (eg - if we support 16x we support
8x and 4x, etc)

BUG=angleproject:1014

Change-Id: I62143e5db561b717edd1a0c96f5e3acd4de3d154
Reviewed-on: https://chromium-review.googlesource.com/275777Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>