Add tests where we split near an edge.

cc/quads/draw_polygon.h

Index: cc/quads/draw_polygon.h
diff --git a/cc/quads/draw_polygon.h b/cc/quads/draw_polygon.h
index 2dc642cde3195cd8beb47c74b72476cfb9ba1a5f..3babcca02e045aa0b1682b0b6aa0ed12eed880d8 100644
--- a/cc/quads/draw_polygon.h
+++ b/cc/quads/draw_polygon.h
@@ -56,7 +56,10 @@ class CC_EXPORT DrawPolygon {
   bool is_split() const { return is_split_; }
   std::unique_ptr<DrawPolygon> CreateCopy();
 
+  // These are helper functions for testing.
   void RecomputeNormalForTesting();
+  bool IsPlanarForTesting() const;
+  bool IsConvexForTesting() const;
 
  private:
   void ApplyTransform(const gfx::Transform& transform);