Replace inverse transform with Cross-product computation.

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 93c36024fc24562b5303e3b30591ddd77543c411..668d9f2dc28e1de89c30243b30929d5a3ae4216a 100644
--- a/cc/quads/draw_polygon.h
+++ b/cc/quads/draw_polygon.h
@@ -59,10 +59,14 @@ class CC_EXPORT DrawPolygon {
   bool is_split() const { return is_split_; }
   scoped_ptr<DrawPolygon> CreateCopy();
 
+  void RecomputeNormalForTesting();
+
  private:
   void ApplyTransform(const gfx::Transform& transform);
   void ApplyTransformToNormal(const gfx::Transform& transform);
 
+  void ConstructNormal();
+
   std::vector<gfx::Point3F> points_;
   // Normalized, necessitated by distance calculations and tests of coplanarity.
   gfx::Vector3dF normal_;