Add GM::onceBeforeDraw method that encapsulates calling onOnceBeforeDraw

This is pulled out of the gpuSetup refactoring in an attempt to break it into simpler bits.

Change-Id: I01e1717b7f046ad4b87a3f38ac201347a51041ff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299077
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
5 files changed