Fix row-major layout tracking in interface blocks. Some block field types, such as nested structs, were bugged. This only affects our "CollectVariables" path, not our current HLSL UBO path. BUG=angle:466 Change-Id: I2b8daf58aa7ec1ad06a80d38f57e76087eacccdc Reviewed-on: https://chromium-review.googlesource.com/213503 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Nicolas Capens <capn@chromium.org>