DM: add --writePath

For fun, make the output prettier, hiding ", N failures" unless there is one.

BUG=
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/29293003

git-svn-id: http://skia.googlecode.com/svn/trunk@11867 2bbb7eff-a529-9590-31e7-b0007b416f81
8 files changed