Move more internal methods from GrContext to GrContextPriv

TBR=bsalomon@google.com
Change-Id: Ia8cf0e0d30451c69bc7a08215aafa6abe6e0ddbe
Reviewed-on: https://skia-review.googlesource.com/97080
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
36 files changed