GM: add --writeChecksumBasedFilenames option 

as needed for Step 2 of https://goto.google.com/ChecksumTransitionDetail :
make GenerateGMs upload actual images to Google Storage instead of skia-autogen

R=scroggo@google.com

Review URL: https://codereview.chromium.org/17365002

git-svn-id: http://skia.googlecode.com/svn/trunk@9682 2bbb7eff-a529-9590-31e7-b0007b416f81
13 files changed