Add a shader cap for incomplete short int precision

Bug: skia:
Change-Id: Iac36eb763e687f6ecc3acbd4afced66f95596be2
Reviewed-on: https://skia-review.googlesource.com/109003
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
6 files changed