Make the buttons on home.dart fill the screen width again

sky/home.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:sky';
 
 import 'package:mojom/intents/intents.mojom.dart';
 import 'package:sky/framework/shell.dart' as shell;
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/theme/edges.dart';
@@ skipping 20 matching lines @@
   String text;
   String href;
 
   SkyDemo(String text, this.href) : this.text = text, super(key: text);
 
   void _handlePress() {
     launch(href);
   }
 
   UINode build() {
-    return new RaisedButton(
-      child: new Text(text),
-      onPressed: _handlePress
+    return new ConstrainedBox(
+      // TOOD(ianh): Fix so we don't need INFINITY here.
+      constraints: new BoxConstraints.tightFor(width: double.INFINITY),
+      child: new RaisedButton(
+        child: new Text(text),
+        onPressed: _handlePress
+      )
     );
   }
 }
 
 class SkyHome extends App {
   UINode build() {
     List<UINode> children = [
       new SkyDemo('Stocks App', 'examples/stocks2/lib/stock_app.dart'),
       new SkyDemo('Astroids Game', 'examples/game/main.dart'),
       new SkyDemo('Interactive Flex', 'examples/rendering/interactive_flex.dart'),
@@ skipping 20 matching lines @@
           justifyContent: FlexJustifyContent.spaceAround
         )
       )
     );
   }
 }
 
 void main() {
   runApp(new SkyHome());
 }