use validating readbuffer

Bug:784869
Change-Id: Iaf43e14ec2ad72d061e7de25364fb481229d7651
Reviewed-on: https://skia-review.googlesource.com/71764
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
1 file changed