Support for background images on cards, style demo home

sky/sdk/lib/widgets/scrollable.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 '../animation/generators.dart';
 import '../animation/mechanics.dart';
 import '../animation/scroll_behavior.dart';
-import '../theme/edges.dart';
 import '../theme/view_configuration.dart' as config;
 import 'basic.dart';
 import 'material.dart';
 
 const double _kMillisecondsPerSecond = 1000.0;
 
 double _velocityForFlingGesture(sky.GestureEvent event) {
   return math.max(-config.kMaxFlingVelocity, math.min(config.kMaxFlingVelocity,
       -event.velocityY)) / _kMillisecondsPerSecond;
 }
@@ skipping 133 matching lines @@
 
   void _handleFlingCancel(sky.GestureEvent event) {
     _startSimulation(_createParticle());
   }
 
   void _handleWheel(sky.WheelEvent event) {
     scrollBy(-event.offsetY);
   }
 
 }