Scroll offset animation curve retargeting.

ui/gfx/geometry/cubic_bezier.h

Index: ui/gfx/geometry/cubic_bezier.h
diff --git a/ui/gfx/geometry/cubic_bezier.h b/ui/gfx/geometry/cubic_bezier.h
index 645dfb7106de68d0cf001a4175cb364c45b409b5..66d5e8a514012c623c3f8d9152599cd9e355183e 100644
--- a/ui/gfx/geometry/cubic_bezier.h
+++ b/ui/gfx/geometry/cubic_bezier.h
@@ -18,6 +18,9 @@ class GFX_EXPORT CubicBezier {
   // Returns an approximation of y at the given x.
   double Solve(double x) const;
 
+  // Returns an approximation of dy/dx at the given x.
+  double Slope(double x) const;
+
   // Sets |min| and |max| to the bezier's minimum and maximium y values in the
   // interval [0, 1].
   void Range(double* min, double* max) const;