experiment with zero-length round capped line segments

include/core/SkPaint.h

Index: include/core/SkPaint.h
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index 1b993fc5ea8a92b947d3d48355b329917265b22b..0c071ad361416c859fa006db17395cae79e43e1b 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -398,6 +398,15 @@ public:
     /** Cap enum specifies the settings for the paint's strokecap. This is the
         treatment that is applied to the beginning and end of each non-closed
         contour (e.g. lines).
+
+        If the cap is round or square, the caps are drawn when the contour has
+        a zero length. Zero length contours can be created by following moveTo
+        with a lineTo at the same point, or a moveTo followed by a close.
+
+        A dash with an on interval of zero also creates a zero length contour.
+
+        The zero length contour draws the square cap without rotation, since
+        the no direction can be inferred.
     */
     enum Cap {
         kButt_Cap,      //!< begin/end contours with no extension