add --modulo A B option to gm, so we can only execute 1/B of the tests in a 
given instance.
Review URL: https://codereview.appspot.com/6739044

git-svn-id: http://skia.googlecode.com/svn/trunk@6007 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed