Add DiffReport so that rendertest could also report more info.

R=bsheedy@chromium.org, harringtond@chromium.org, peconn@chromium.org

Bug: 1035587
Change-Id: Ib3cff9d9fef0b474e53d0e9023f4d03b97f73d37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1977389
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Commit-Queue: Arthur Wang <wuwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728983}
1 file changed