Fixed some bugs for flutter tests Change-Id: I43f4b4b185152a8d642127370da5f80fb96f1e9e Reviewed-on: https://skia-review.googlesource.com/c/skia/+/239444 Commit-Queue: Julia Lavrova <jlavrova@google.com> Reviewed-by: Ben Wagner <bungeman@google.com>