Make sure that the type definitions for nested structs get added to
the HLSL header, and that the std140 padding information gets
recorded. Prior to this trying to use nested structs in interface
blocks crashed.

BUG=angleproject:2084
TEST=angle_end2end_tests

Change-Id: If57870285c6feaf0c2e462f98f50f20730dd6470
Reviewed-on: https://chromium-review.googlesource.com/608449Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>