Support for background images on cards, style demo home

sky/sdk/lib/widgets/widget.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:collection';
 import 'dart:mirrors';
 import 'dart:sky' as sky;
 
 import '../base/hit_test.dart';
@@ skipping 261 matching lines @@
   }
 }
 
 typedef void GestureEventListener(sky.GestureEvent e);
 typedef void PointerEventListener(sky.PointerEvent e);
 typedef void EventListener(sky.Event e);
 
 class Listener extends TagNode  {
 
   Listener({
+    String key,
     Widget child,
     EventListener onWheel,
     GestureEventListener onGestureFlingCancel,
     GestureEventListener onGestureFlingStart,
     GestureEventListener onGestureScrollStart,
     GestureEventListener onGestureScrollUpdate,
     GestureEventListener onGestureTap,
     GestureEventListener onGestureTapDown,
     PointerEventListener onPointerCancel,
     PointerEventListener onPointerDown,
     PointerEventListener onPointerMove,
     PointerEventListener onPointerUp,
     Map<String, sky.EventListener> custom
   }) : listeners = _createListeners(
          onWheel: onWheel,
          onGestureFlingCancel: onGestureFlingCancel,
          onGestureFlingStart: onGestureFlingStart,
          onGestureScrollUpdate: onGestureScrollUpdate,
          onGestureScrollStart: onGestureScrollStart,
          onGestureTap: onGestureTap,
          onGestureTapDown: onGestureTapDown,
          onPointerCancel: onPointerCancel,
          onPointerDown: onPointerDown,
          onPointerMove: onPointerMove,
          onPointerUp: onPointerUp,
          custom: custom
        ),
-       super(child);
+       super(child, key: key);
 
   final Map<String, sky.EventListener> listeners;
 
   static Map<String, sky.EventListener> _createListeners({
     EventListener onWheel,
     GestureEventListener onGestureFlingCancel,
     GestureEventListener onGestureFlingStart,
     GestureEventListener onGestureScrollStart,
     GestureEventListener onGestureScrollUpdate,
     GestureEventListener onGestureTap,
@@ skipping 693 matching lines @@
     if (root.parent == null) {
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   Widget build() => builder();
 }