use safemath::mull for buffer sizes

Bug:780104
Change-Id: Ic683abd9c7d15ebb01b6e5d40dbeb6e76f102eff
Reviewed-on: https://skia-review.googlesource.com/95760
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
(cherry picked from commit fe266c2bce2b8ac4ef953f16c8e1a7801da9c57d)
Reviewed-on: https://skia-review.googlesource.com/101780
Reviewed-by: Mike Reed <reed@google.com>
1 file changed