Centralize error checking w/in the GrProgramInfo class

Although not necessary I would like to centralize/encapsulate the error checking so there is just one place to go to update/extend this code. It does have the nice property that, since we validate in the ctor and this object is immutable, we only have to do it once (and can delete some code spread throughout the code base).

Bug: skia:9455
Change-Id: Iaa26c7a896a9bd053358a6f8424d7f5944b0117e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247339
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed