Sometimes the drawer doesn't fully close

sky/framework/animation/generator.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.
 
 import 'curves.dart';
 import 'dart:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 class FrameGenerator {
@@ skipping 55 matching lines @@
     this.curve: linear,
     Function onDone
   }):super(onDone: onDone) {
     double startTime = 0.0;
     _stream = super.onTick.map((timeStamp) {
       if (startTime == 0.0)
         startTime = timeStamp;
       return math.min((timeStamp - startTime) / duration, 1.0);
     })
     .takeWhile(_checkForCompletion)
-    .map((t) =>  begin + (end - begin) * curve.transform(t));
+    .map(_transform);
+  }
+
+  double _transform(double t) {
+    if (_done)
+      return end;
+    return begin + (end - begin) * curve.transform(t);
   }
 
   bool _checkForCompletion(double t) {
     if (_done)
       return false;
     _done = t >= 1;
     return true;
   }
 }