Take into account fill-rule for polygon interpolation

Implement the polygon fill-rule part of http://dev.w3.org/csswg/css-shapes/#basic-shape-interpolation.

Review URL: https://codereview.chromium.org/132643006

git-svn-id: svn://svn.chromium.org/blink/trunk@165082 bbb929c8-8fbe-4397-9dbb-9b2b20218538