Scroll offset animation curve retargeting.

ui/gfx/geometry/cubic_bezier.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_GEOMETRY_CUBIC_BEZIER_H_
 #define UI_GFX_GEOMETRY_CUBIC_BEZIER_H_
 
 #include "base/macros.h"
 #include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 
 class GFX_EXPORT CubicBezier {
  public:
   CubicBezier(double x1, double y1, double x2, double y2);
   ~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;
 
  private:
   double x1_;
   double y1_;
   double x2_;
   double y2_;
 
   DISALLOW_ASSIGN(CubicBezier);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_CUBIC_BEZIER_H_