Get baselines from cached default metrics if the text is empty

Change-Id: Ic04251d60d6d36f80c3e569312495190ba375d85
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/258488
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Jason Simmons <jsimmons@google.com>
3 files changed