added support for flat and noperspective modifiers in SPIR-V

Bug: skia:
Change-Id: I41f90464377be5de6813d6011b7e53dbac9230b6
Reviewed-on: https://skia-review.googlesource.com/26345
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed