Make back button control drawer in stocks app

sky/sdk/lib/widgets/drawer.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 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import '../animation/animated_value.dart';
@@ skipping 36 matching lines @@
   void _checkValue() {
     var newClosedState = isClosed;
     if (onStatusChange != null && _oldClosedState != newClosedState) {
       onStatusChange(!newClosedState);
       _oldClosedState = newClosedState;
     }
   }
 
   bool get isClosed => position.value == -_kWidth;
   bool get _isMostlyClosed => position.value <= -_kWidth / 2;
-  void toggle() => _isMostlyClosed ? _open() : _close();
+  void toggle() => _isMostlyClosed ? open() : close();
 
-  void handleMaskTap(_) => _close();
+  void handleMaskTap(_) => close();
   void handlePointerDown(_) => position.stop();
 
   void handlePointerMove(sky.PointerEvent event) {
     if (position.isAnimating)
       return;
     position.value = math.min(0.0, math.max(position.value + event.dx, -_kWidth));
   }
 
   void handlePointerUp(_) {
     if (!position.isAnimating)
       _settle();
   }
 
   void handlePointerCancel(_) {
     if (!position.isAnimating)
       _settle();
   }
 
-  void _open() => _animateToPosition(0.0);
+  void open() => _animateToPosition(0.0);
 
-  void _close() => _animateToPosition(-_kWidth);
+  void close() => _animateToPosition(-_kWidth);
 
-  void _settle() => _isMostlyClosed ? _close() : _open();
+  void _settle() => _isMostlyClosed ? close() : open();
 
   void _animateToPosition(double targetPosition) {
     double distance = (targetPosition - position.value).abs();
     if (distance != 0) {
       double targetDuration = distance / _kWidth * _kBaseSettleDurationMS;
       double duration = math.min(targetDuration, _kMaxSettleDurationMS);
       position.animateTo(targetPosition, duration, curve: _kAnimationCurve);
     }
   }
 
@@ skipping 64 matching lines @@
     return new Listener(
       child: new Stack([ mask, content ]),
       onPointerDown: controller.handlePointerDown,
       onPointerMove: controller.handlePointerMove,
       onPointerUp: controller.handlePointerUp,
       onPointerCancel: controller.handlePointerCancel
     );
   }
 
 }