Move stub methods for updating shader into base

Change-Id: I2069553795403ea85e51eb84d4b146d10e59b027
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/434296
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed