Make the drawer, popup menus, dialogs, and settings page scrollable.

sky/engine/core/painting/OffsetBase.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.
 
 part of dart.sky;
 
 abstract class OffsetBase {
   const OffsetBase(this._dx, this._dy);
 
   final double _dx;
   final double _dy;
 
   bool get isInfinite => _dx >= double.INFINITY || _dy >= double.INFINITY;
 
+  bool operator <(OffsetBase other) => _dx < other._dx && _dy < other._dy;
+  bool operator <=(OffsetBase other) => _dx <= other._dx && _dy <= other._dy;
+  bool operator >(OffsetBase other) => _dx > other._dx && _dy > other._dy;
+  bool operator >=(OffsetBase other) => _dx > other._dx && _dy >= other._dy;
+
   bool operator ==(other) {
     return other is OffsetBase &&
            other.runtimeType == runtimeType &&
            other._dx == _dx &&
            other._dy == _dy;
   }
 
   int get hashCode {
     int result = 373;
     result = 37 * result + _dx.hashCode;
     result = 37 * result + _dy.hashCode;
     return result;
   }
 }