use pathops utils to improve precision of cubic chopping in scan converter

src/core/SkEdgeClipper.cpp

Index: src/core/SkEdgeClipper.cpp
diff --git a/src/core/SkEdgeClipper.cpp b/src/core/SkEdgeClipper.cpp
index 32277bcf8e3cc89064dc834a07add63efc6558f0..2b3bf073b174129a78050e70bc63714baabf16db 100644
--- a/src/core/SkEdgeClipper.cpp
+++ b/src/core/SkEdgeClipper.cpp
@@ -267,9 +267,11 @@ static bool chopMonoCubicAt(SkScalar c0, SkScalar c1, SkScalar c2, SkScalar c3,
     return true;
 }
 
+#if 0
 static bool chopMonoCubicAtY(SkPoint pts[4], SkScalar y, SkScalar* t) {
     return chopMonoCubicAt(pts[0].fY, pts[1].fY, pts[2].fY, pts[3].fY, y, t);
 }
+#endif
 
 static bool chopMonoCubicAtX(SkPoint pts[4], SkScalar x, SkScalar* t) {
     return chopMonoCubicAt(pts[0].fX, pts[1].fX, pts[2].fX, pts[3].fX, x, t);
@@ -280,17 +282,20 @@ static void chop_cubic_in_Y(SkPoint pts[4], const SkRect& clip) {
 
     // are we partially above
     if (pts[0].fY < clip.fTop) {
+        SkPoint tmp[7];
+#if 0
         SkScalar t;
         if (chopMonoCubicAtY(pts, clip.fTop, &t)) {
-            SkPoint tmp[7];
             SkChopCubicAt(pts, tmp, t);
-
+#else
+        if (SkChopMonoCubicAtY(pts, clip.fTop, tmp)) {
+#endif
             // tmp[3, 4, 5].fY should all be to the below clip.fTop.
             // Since we can't trust the numerics of
             // the chopper, we force those conditions now
             tmp[3].fY = clip.fTop;
             clamp_ge(tmp[4].fY, clip.fTop);
-            clamp_ge(tmp[5].fY, clip.fTop);
+     //       clamp_ge(tmp[5].fY, clip.fTop);
 
             pts[0] = tmp[3];
             pts[1] = tmp[4];
@@ -306,10 +311,14 @@ static void chop_cubic_in_Y(SkPoint pts[4], const SkRect& clip) {
 
     // are we partially below
     if (pts[3].fY > clip.fBottom) {
+        SkPoint tmp[7];
+#if 0
         SkScalar t;
         if (chopMonoCubicAtY(pts, clip.fBottom, &t)) {
-            SkPoint tmp[7];
             SkChopCubicAt(pts, tmp, t);
+#else
+        if (SkChopMonoCubicAtY(pts, clip.fBottom, tmp)) {
+#endif
             tmp[3].fY = clip.fBottom;
             clamp_le(tmp[2].fY, clip.fBottom);