Separate invariance from qualifiers ESSL3 makes it possible to combine invariant with several more different qualifiers. To avoid combinatorial explosion of the qualifier enum, track invariance with a separate boolean. TEST=WebGL conformance tests, angle_unittests BUG=angleproject:987 Change-Id: I0c6629e5ca2ded06db9ac9e5bab2fb6480299a5a Reviewed-on: https://chromium-review.googlesource.com/267662 Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com>