Define accelerated steps time function.

ui/gfx/animation/steps.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_STEPS_H_
+#define UI_GFX_GEOMETRY_STEPS_H_
+
+#include "base/macros.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+class GFX_EXPORT Steps {
+ public:
+  Steps(int steps, bool steps_at_start);
+  ~Steps();
+
+  // Returns y at the given x.
+  double Solve(double x) const;
+
+  // Sets |min| and |max| to the step functions's minimum and maximium y values
+  // in the interval [0, 1].
+  void Range(double* min, double* max) const;
+
+ private:
+  int steps_;
+  bool steps_at_start_;
+
+  DISALLOW_ASSIGN(Steps);
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_GEOMETRY_STEPS_H_