Add VR Shell animation classes and unit test.

chrome/browser/android/vr_shell/easing.cc

+// 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.
+
+#include "chrome/browser/android/vr_shell/easing.h"
+
+#include <cmath>
+
+namespace vr_shell {
+namespace easing {
+
+CubicBezier::CubicBezier(double p1x, double p1y, double p2x, double p2y)
+    : bezier_(p1x, p1y, p2x, p2y) {}
+
+double CubicBezier::CalculateValue(double state) {
+  return bezier_.Solve(state);

[David Trainor- moved to gerrit, 2016/09/14 21:43:29]

Do we want to DCHECK or clamp state for all of these?

[cjgrant, 2016/09/16 17:47:07]

I refactored this to let the check live in the base class.  Let me know if you
like this better.

+}
+
+EaseIn::EaseIn(double power) : power_(power) {}
+double EaseIn::CalculateValue(double state) {
+  return pow(state, power_);
+}
+
+EaseOut::EaseOut(double power) : power_(power) {}
+double EaseOut::CalculateValue(double state) {
+  return 1.0 - pow(1.0 - state, power_);
+}
+
+double Linear::CalculateValue(double state) {
+  return state;
+}
+
+}  // namespace easing
+}  // namespace vr_shell