gm: change ErrorBitfield to ErrorType/ErrorCombination
This will enable future GM changes to report errors more completely/consistently, like skdiff.
Review URL: https://codereview.chromium.org/12992003

git-svn-id: http://skia.googlecode.com/svn/trunk@8344 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed