Port sky-drawer to Dart

sky/framework/animation/curves.sky

-<!--
-// Copyright 2015 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.
--->
-<script>
-function evaluateCubic(a, b, m) {
-  // TODO(abarth): Would Math.pow be faster?
-  return 3 * a * (1 - m) * (1 - m) * m + 3 * b * (1 - m) * m * m + m * m * m
-}
-
-const kCubicErrorBound = 0.001;
-
-class Linear {
-  transform(t) {
-    return t;
-  }
-};
-
-class Cubic {
-  constructor(a, b, c, d) {
-    this.a_ = a;
-    this.b_ = b;
-    this.c_ = c;
-    this.d_ = d;
-    Object.preventExtensions(this);
-  }
-
-  transform(t) {
-    var start = 0, end = 1;
-    while (1) {
-      var midpoint = (start + end) / 2;
-      var estimate = evaluateCubic(this.a_, this.c_, midpoint);
-
-      if (Math.abs(t - estimate) < kCubicErrorBound)
-        return evaluateCubic(this.b_, this.d_, midpoint);
-
-      if (estimate < t)
-        start = midpoint;
-      else
-        end = midpoint;
-    }
-  }
-}
-
-module.exports = {
-  Linear: Linear,
-  Cubic: Cubic,
-  linear: new Linear(),
-  ease: new Cubic(0.25, 0.1, 0.25, 1),
-  easeIn: new Cubic(0.42, 0, 1, 1),
-  easeOut: new Cubic(0, 0, 0.58, 1),
-  easeInOut: new Cubic(0.42, 0, 0.58, 1),
-};
-</script>