GrGLProgramBuilder cleanup

Only call addInputVars and computeCountsAndStrides in one place
(we were calling the latter twice when getting GLSL from the
cache, for some reason).

Add/edit some better comments.

Change-Id: I860fa241fc89a33cd5da243d0b549a5a5b5b88cf
Bug: skia:9402
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/243658
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed