Update BoxDecoration and RenderParagraph to use sky.Color instead of int.

sky/sdk/lib/framework/rendering/box.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 'dart:typed_data';
 import 'node.dart';
 import 'package:vector_math/vector_math.dart';
 
@@ skipping 233 matching lines @@
         child.hitTest(result, position: new sky.Point(position.x - child.parentData.position.x,
                                                       position.y - child.parentData.position.y));
       }
     }
   }
 
 }
 
 // This must be immutable, because we won't notice when it changes
 class BoxDecoration {
-  // TODO(mpcomplete): go through and change the users of this class to pass
-  // a Color object.
-  BoxDecoration({
-    backgroundColor
-  }) : backgroundColor = new sky.Color(backgroundColor);
+  const BoxDecoration({this.backgroundColor});
 
   final sky.Color backgroundColor;
 }
 
 class RenderDecoratedBox extends RenderProxyBox {
 
   RenderDecoratedBox({
     BoxDecoration decoration,
     RenderBox child
   }) : _decoration = decoration, super(child);
@@ skipping 192 matching lines @@
 
   void defaultPaint(RenderNodeDisplayList canvas) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position);
       child = child.parentData.nextSibling;
     }
   }
 }