Move more internal methods from GrContext to GrContextPriv (take 3)

Change-Id: Ied630e61cf95780bf85032867e6ce663e1ef9c2f
Reviewed-on: https://skia-review.googlesource.com/98000
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
35 files changed