Implement a simple checkbox in Sky’s fn2 components library

sky/engine/core/painting/Canvas.idl

Index: sky/engine/core/painting/Canvas.idl
diff --git a/sky/engine/core/painting/Canvas.idl b/sky/engine/core/painting/Canvas.idl
index ae833fcd321d0df74a3a72e21e25d01186a337dc..876156e54f0ee568fc82eceef4de5b3f6473a971 100644
--- a/sky/engine/core/painting/Canvas.idl
+++ b/sky/engine/core/painting/Canvas.idl
@@ -21,10 +21,11 @@ interface Canvas {
 
   void clipRect(Rect rect);
 
+  void drawLine(float x0, float y0, float x1, float y1, Paint paint);
   void drawPicture(Picture picture);
-
   void drawPaint(Paint paint);
   void drawRect(Rect rect, Paint paint);
+  void drawRRect(RRect rrect, Paint paint);
   void drawOval(Rect rect, Paint paint);
   void drawCircle(float x, float y, float radius, Paint paint);
   void drawPath(Path path, Paint paint);