gpu: Expose GrContextPriv::abandoned in the public API.

TBR=bsalomon@google.com

Bug: 854416
Change-Id: Iab71ca6e4724a925b0b9791267aac5ddc34f5b15
Reviewed-on: https://skia-review.googlesource.com/137692
Reviewed-by: Khusal Sagar <khushalsagar@chromium.org>
Commit-Queue: Khusal Sagar <khushalsagar@chromium.org>
14 files changed