Add private GrContext::compile API

Currently this is only implemented for GL.

Bug: skia:9455
Change-Id: I8f369273b697e80a4bade5dd2283e66df688f0ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271742
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
13 files changed