Fix simple-magnification GM in "--preAbandonGpuContext" mode

Change-Id: Ia225464e9c58a0aeb2f63b7ca5d5025fc6891598
Reviewed-on: https://skia-review.googlesource.com/8260
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed