Revert of Remove unnecessary static function

cc/trees/layer_sorter.cc

Index: cc/trees/layer_sorter.cc
diff --git a/cc/trees/layer_sorter.cc b/cc/trees/layer_sorter.cc
index 8f3454e8514957ff47c5d194b62b4e65e64efa63..e171fe01120f6389931b1acb403581968e7126db 100644
--- a/cc/trees/layer_sorter.cc
+++ b/cc/trees/layer_sorter.cc
@@ -22,6 +22,11 @@
 // a value near machine epsilon and then increasing it until the flickering on
 // the test scene went away.
 const float k_layer_epsilon = 1e-4f;
+
+inline static float PerpProduct(const gfx::Vector2dF& u,
+                                const gfx::Vector2dF& v) {
+  return u.x() * v.y() - u.y() * v.x();
+}
 
 // Tests if two edges defined by their endpoints (a,b) and (c,d) intersect.
 // Returns true and the point of intersection if they do and false otherwise.
@@ -34,7 +39,7 @@
   gfx::Vector2dF v = d - c;
   gfx::Vector2dF w = a - c;
 
-  float denom = static_cast<float>(gfx::CrossProduct(u, v));
+  float denom = PerpProduct(u, v);
 
   // If denom == 0 then the edges are parallel. While they could be overlapping
   // we don't bother to check here as the we'll find their intersections from
@@ -42,11 +47,11 @@
   if (!denom)
     return false;
 
-  float s = static_cast<float>(gfx::CrossProduct(v, w)) / denom;
+  float s = PerpProduct(v, w) / denom;
   if (s < 0.f || s > 1.f)
     return false;
 
-  float t = static_cast<float>(gfx::CrossProduct(u, w)) / denom;
+  float t = PerpProduct(u, w) / denom;
   if (t < 0.f || t > 1.f)
     return false;