This CL depends on
https://codereview.chromium.org/12880016/
"Add intersections for path ops"
Given a path, iterate through its contour, and
construct an array of segments containing its curves.
Intersect each curve with every other curve, and for
cubics, with itself.
Given the set of intersections, find one with the
smallest y and sort the curves eminating from the
intersection. Assign each curve a winding value.
Operate on the curves, keeping and discarding them
according to the current operation and the sum of
the winding values.
Assemble the kept curves into an output path.
Review URL: https://codereview.chromium.org/13094010
git-svn-id: http://skia.googlecode.com/svn/trunk@8553 2bbb7eff-a529-9590-31e7-b0007b416f81
