Improve the curve tessellation subdivision of the path renderers.

src/gpu/GrPathUtils.h

Index: src/gpu/GrPathUtils.h
diff --git a/src/gpu/GrPathUtils.h b/src/gpu/GrPathUtils.h
index c15fd7ae103237f8a4ecfda44d9fbf95dcd47e64..250b0a23245a2b81c22e73fb6e97e70ae0333b19 100644
--- a/src/gpu/GrPathUtils.h
+++ b/src/gpu/GrPathUtils.h
@@ -168,5 +168,12 @@ namespace GrPathUtils {
     // If you transform the points the lines will also need to be transformed. This can be done
     // by mapping the lines with the inverse-transpose of the matrix used to map the points.
     void getCubicKLM(const SkPoint p[4], SkScalar klm[9]);
+
+    // When tessellating curved paths into linear segments, this defines the maximum distance
+    // in screen space which a segment may deviate from the mathmatically correct value.
+    // Above this value, the segment will be subdivided.
+    // This value was chosen to approximate the supersampling accuracy of the raster path (16
+    // samples, or one quarter pixel).
+    static const SkScalar kDefaultTolerance = SkDoubleToScalar(0.25);
 };
 #endif