[canvaskit] Fix flaky test

We accidentally were not waiting until all font files were loaded before
trying to process them.

Bug: skia:9858
Change-Id: I10decd5fbf0aa46e300d2ce5255f24f1ac1c12d4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268626
Reviewed-by: Nathaniel Nifong <nifong@google.com>
1 file changed