fix path op builder

The rewrite of path ops caused the inner contour direction to be reversed.
This exposed an existing bug in path ops builder, namely that the implicit
winding of the internal sum path could hide inner contours if they ended
up in the wrong direction.

Setting the sum path's fill type to even-odd ensures that the inner
contours aren't discarded.

R=fmalita@chromium.org
BUG=skia:3838

Review URL: https://codereview.chromium.org/1126193004
3 files changed