This patch outputs switch and case statements in HLSL, but ignores fall-through.
Switch statements that include fall-through cause the platform HLSL compiler to
generate errors.

BUG=angle:921

Change-Id: I10efbfb45076cf4fd79840698abafd8111e597d4
Reviewed-on: https://chromium-review.googlesource.com/251527Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>