Migrate SkImage::flush methods to GrDirectContext

Flag landed in Chrome CL 2310889.

Bug: skia:104662
Change-Id: I616c7e6cd16104132bb0764c6d786a5cbeb4dd47
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304797
Commit-Queue: Adlai Holler <adlai@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
7 files changed