gm self-test: make all test cases exercise transparency
BUG=https://code.google.com/p/skia/issues/detail?id=1142
Review URL: https://codereview.chromium.org/12379047

git-svn-id: http://skia.googlecode.com/svn/trunk@7943 2bbb7eff-a529-9590-31e7-b0007b416f81
18 files changed