Don't execute onFlush op lists until after GPU data is uploaded

Bug: skia:
Change-Id: Ide85e802fd6e6a19412457dbaded3545b962c240
Reviewed-on: https://skia-review.googlesource.com/55562
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed