Update error handling in DDL-averse GMs

This will allow local debug DDL dm runs to complete.

Change-Id: I47aa978c5e52fd1dcdba45c59318844bae871115
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/326796
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed