Handle allocation failure in the flush-time preFlush callback

In general, we drop the entire flush when we detect an allocation
failure. This CL makes an allocation failure in the flush-time preFlush
call also drop the entire flush.

Bug: 1320964
Change-Id: Idd2e24fbf5d2083c4fec8de7ccd028897a239b33
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/536837
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
13 files changed