Split GrContext into Normal/DDL flavors

Change-Id: If37d8a236bd71e2d7121eaafb9d7c7b08328b10f
Reviewed-on: https://skia-review.googlesource.com/84863
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
9 files changed