Perform BSP polygon splitting and orientation selection in a single step.

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 b3bde398c5556533d80deba71f0c030f64e8be30..eae0f2ee1a42d55622d83dbdc3a45e16a198201f 100644
--- a/cc/quads/draw_polygon.h
+++ b/cc/quads/draw_polygon.h
@@ -40,9 +40,12 @@ class CC_EXPORT DrawPolygon {
   // Split will only return true if it determines that we got back 2
   // intersection points. Only when it returns true will front and back both be
   // valid new polygons that are on opposite sides of the splitting plane.
-  bool Split(const DrawPolygon& splitter,
-             std::unique_ptr<DrawPolygon>* front,
-             std::unique_ptr<DrawPolygon>* back);
+  bool SplitPolygon(std::unique_ptr<DrawPolygon> polygon,

[enne (OOO), 2016/06/08 22:02:51]

Style nit: if you have more than one out parameter, then make them all
parameters and not some as out parameters and one as a return value.

I see you're using it for EXPECT calls, but it looks like you could write a test
helper that says bool IsCoplanar() and hides the front and back parameters
inside it, and checks that front and back are not null when a split occurs.

[Tobias Sargeant, 2016/06/09 16:48:44]

Done.

+                    std::unique_ptr<DrawPolygon>* front,
+                    std::unique_ptr<DrawPolygon>* back);
+  bool SplitPolygon(const DrawPolygon& polygon,

[enne (OOO), 2016/06/08 22:02:51]

This is a bit awkward.  How many test locations use this? Can you just make the
test call WrapUnique or move this function into tests?

[Tobias Sargeant, 2016/06/09 16:48:44]

Moved this into the tests.

+                    std::unique_ptr<DrawPolygon>* front,
+                    std::unique_ptr<DrawPolygon>* back);
   float SignedPointDistance(const gfx::Point3F& point) const;
   // Checks polygon a against polygon b and returns which side it lies on, or
   // whether it crosses (necessitating a split in the BSP tree).