Hiding cast of WebCore WindRule to SkPath::FillType

Adding a inline helper function in SkiaUtils.h to hide the cast of WebCore Windrule to SkPath::FillType

Review URL: https://codereview.chromium.org/453233002

git-svn-id: svn://svn.chromium.org/blink/trunk@179968 bbb929c8-8fbe-4397-9dbb-9b2b20218538