Add visual tests for stat_density2d

Author: wch

visual_test/geom-polygon.r

@@ -0,0 +1,13 @@
+vcontext("geom-polygon")
+
+ggplot(faithful, aes(x = eruptions, y = waiting)) +
+  stat_density2d(aes(colour = ..level..), geom="path") +
+  xlim(0.5, 6) + ylim(40, 110)
+save_vtest("stat_density2d with paths")
+
+ggplot(faithful, aes(x = eruptions, y = waiting)) +
+  stat_density2d(aes(fill = ..level..), geom="polygon", colour="white") +
+  xlim(0.5, 6) + ylim(40, 110)
+save_vtest("stat_density2d with filled polygons")
+
+end_vcontext()