- input param to addFoo (e.g. addRect), where only CW or CCW are valid)
- output param from computing functions, that sometimes return kUnknown
This CL's intent is to split these into distinct enums/features:
- Direction (public) loses kUnknown, and is only used for input
- FirstDirection (private) is used for computing the first direction we see when analyzing a contour
BUG=skia:
Review URL: https://codereview.chromium.org/1176953002
