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

src/core/SkGeometry.h

Index: src/core/SkGeometry.h
diff --git a/src/core/SkGeometry.h b/src/core/SkGeometry.h
index 811678eeec79b78eafb7166849c396ff98f25d36..a0c13d6046d95fa15d6d96a30fc3b044d703fbc6 100644
--- a/src/core/SkGeometry.h
+++ b/src/core/SkGeometry.h
@@ -166,6 +166,9 @@ int SkFindCubicMaxCurvature(const SkPoint src[4], SkScalar tValues[3]);
 int SkChopCubicAtMaxCurvature(const SkPoint src[4], SkPoint dst[13],
                               SkScalar tValues[3] = NULL);
 
+bool SkChopMonoCubicAtX(SkPoint src[4], SkScalar y, SkPoint dst[7]);
+bool SkChopMonoCubicAtY(SkPoint src[4], SkScalar x, SkPoint dst[7]);
+
 enum SkCubicType {
     kSerpentine_SkCubicType,
     kCusp_SkCubicType,