Avoid potential overflow in assert.

Bug: chromium:897263
Change-Id: Ida49c4c325974b8a146df93c2c8d6870a1fce64d
Reviewed-on: https://skia-review.googlesource.com/c/164242
Commit-Queue: Ben Wagner <bungeman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Ben Wagner <bungeman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed