Dump out more information if this assert fails.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/ec924b9696277df4c684e73315194482e1d43e50

R=caryclark@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/491903002
1 file changed