DM: add --quiet

This has been handy when tossing in other SkDebugf's.

BUG=
R=bsalomon@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/49323007

git-svn-id: http://skia.googlecode.com/svn/trunk@11998 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed