Make Sky's drawer match Material Design spec

sky/framework/animation/curves.dart

 // 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.
 
 double _evaluateCubic(double a, double b, double 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 double _kCubicErrorBound = 0.001;
 
 abstract class Curve {
   double transform(double t);
 }
 
 class Linear implements Curve {
   const Linear();
 
   double transform(double t) {
     return t;
   }
 }
 
+class ParabolicFall implements Curve {
+  const ParabolicFall();
+
+  double transform(double t) {
+    return -t*t + 1;
+  }
+}
+
+class ParabolicRise implements Curve {
+  const ParabolicRise();
+
+  double transform(double t) {
+    return -(t-1)*(t-1) + 1;
+  }
+}
+
 class Cubic implements Curve {
   final double a;
   final double b;
   final double c;
   final double d;
 
   const Cubic(this.a, this.b, this.c, this.d);
 
   double transform(double t) {
     double start = 0.0;
@@ skipping 11 matching lines @@
         end = midpoint;
     }
   }
 }
 
 const Linear linear = const Linear();
 const Cubic ease = const Cubic(0.25, 0.1, 0.25, 1.0);
 const Cubic easeIn = const Cubic(0.42, 0.0, 1.0, 1.0);
 const Cubic easeOut = const Cubic(0.0, 0.0, 0.58, 1.0);
 const Cubic easeInOut = const Cubic(0.42, 0.0, 0.58, 1.0);
+const Cubic parabolicRise = const ParabolicRise();
+const Cubic parabolicFall = const ParabolicFall();