Add VR Shell animation classes and unit test.

chrome/browser/android/vr_shell/easing.h

+// Copyright 2016 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 CHROME_BROWSER_ANDROID_VR_SHELL_EASING_H_
+#define CHROME_BROWSER_ANDROID_VR_SHELL_EASING_H_
+
+#include "ui/gfx/geometry/cubic_bezier.h"
+
+namespace vr_shell {
+namespace easing {
+
+// Abstract base class for custom interpolators, mapping linear input between
+// 0 and 1 to custom values between those two points.
+class Easing {
+ public:
+  // Compute an output value, given an input between 0 and 1. Output will
+  // equal input at (at least) points 0 and 1.
+  double CalculateValue(double input);
+  virtual ~Easing() {}
+
+ protected:
+  Easing() {}
+  virtual double CalculateValueImpl(double input) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Easing);
+};
+
+// Linear interpolation generates output equal to input.
+class Linear : public Easing {
+ public:
+  Linear() = default;
+  double CalculateValueImpl(double input) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Linear);
+};
+
+// Computes a cubic-bezier transition based on two control points.
+class CubicBezier : public Easing {
+ public:
+  CubicBezier(double p1x, double p1y, double p2x, double p2y);
+  double CalculateValueImpl(double input) override;
+
+ private:
+  gfx::CubicBezier bezier_;
+  DISALLOW_COPY_AND_ASSIGN(CubicBezier);
+};
+
+// Computes |input|^|power|.
+class EaseIn : public Easing {
+ public:
+  explicit EaseIn(double power);
+  double CalculateValueImpl(double input) override;
+
+ private:
+  double power_;
+  DISALLOW_COPY_AND_ASSIGN(EaseIn);
+};
+
+// Computes 1 - |input|^|power|.
+class EaseOut : public Easing {
+ public:
+  explicit EaseOut(double power);
+  double CalculateValueImpl(double input) override;
+
+ private:
+  double power_;
+  DISALLOW_COPY_AND_ASSIGN(EaseOut);
+};
+
+}  // namespace easing
+}  // namespace vr_shell
+
+#endif  // CHROME_BROWSER_ANDROID_VR_SHELL_EASING_H_