Improve the padding and sizing of popup menus.

sky/sdk/lib/widgets/popup_menu.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:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import '../animation/animated_value.dart';
 import '../painting/box_painter.dart';
 import '../theme/colors.dart';
 import '../theme/shadows.dart';
 import 'animated_component.dart';
 import 'basic.dart';
 import 'popup_menu_item.dart';
 
 const double _kMenuOpenDuration = 300.0;
 const double _kMenuCloseDuration = 200.0;
 const double _kMenuCloseDelay = 100.0;
+const double _kMenuWidthStep = 56.0;
+const double _kMenuMinWidth = 1.5 * _kMenuWidthStep;
+const double _kMenuHorizontalPadding = 16.0;
+const double _kMenuVerticalPadding = 8.0;
 
 enum MenuState { hidden, opening, open, closing }
 
 class PopupMenuController {
   AnimatedValue position = new AnimatedValue(0.0);
   MenuState _state = MenuState.hidden;
   MenuState get state => _state;
 
   bool get canReact => (_state == MenuState.opening) || (_state == MenuState.open);
 
@@ skipping 27 matching lines @@
   PopupMenu({ String key, this.controller, this.items, this.level })
       : super(key: key) {
     _painter = new BoxPainter(new BoxDecoration(
       backgroundColor: Grey[50],
       borderRadius: 2.0,
       boxShadow: shadows[level]));
     watch(controller.position);
   }
 
   PopupMenuController controller;
-  List<Widget> items;
+  List<PopupMenuItem> items;
   int level;
 
   void syncFields(PopupMenu source) {
     controller = source.controller;
     items = source.items;
     level = source.level;
     _painter = source._painter;
     super.syncFields(source);
   }
 
@@ skipping 10 matching lines @@
 
   Widget build() {
     int i = 0;
     List<Widget> children = new List.from(items.map((Widget item) {
       double opacity = _opacityFor(i);
       return new PopupMenuItem(child: item, opacity: opacity);
     }));
 
     return new Opacity(
       opacity: math.min(1.0, controller.position.value * 3.0),
-      child: new ShrinkWrapWidth(
-        child: new CustomPaint(
-          callback: (sky.Canvas canvas, Size size) {
-            double width = math.min(size.width, size.width * (0.5 + controller.position.value * 2.0));
-            double height = math.min(size.height, size.height * controller.position.value * 1.5);
-            _painter.paint(canvas, new Rect.fromLTRB(size.width - width, 0.0, width, height));
-          },
-          child: new Container(
-            padding: const EdgeDims.all(8.0),
-            child: new Block(children)
+      child: new CustomPaint(
+        callback: (sky.Canvas canvas, Size size) {
+          double width = math.min(size.width, size.width * (0.5 + controller.position.value * 2.0));
+          double height = math.min(size.height, size.height * controller.position.value * 1.5);
+          _painter.paint(canvas, new Rect.fromLTRB(size.width - width, 0.0, width, height));
+        },
+        child: new ConstrainedBox(
+          constraints: new BoxConstraints(
+            minWidth: _kMenuMinWidth
+          ),
+          child: new ShrinkWrapWidth(
+            stepWidth: _kMenuWidthStep,
+            child: new Container(
+              padding: const EdgeDims.symmetric(
+                horizontal: _kMenuHorizontalPadding,
+                vertical: _kMenuVerticalPadding
+              ),
+              child: new Block(children)
+            )
           )
         )
       )
     );
   }
 
 }