Make RenderParagraph mutable, and make it fit the new RenderNode protocols

sky/examples/raw/render_paragraph.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:sky/framework/app.dart';
 import 'package:sky/framework/layout2.dart';
 
 class RenderSolidColor extends RenderDecoratedBox {
-  final double desiredHeight;
-  final double desiredWidth;
+  final Size desiredSize;
   final int backgroundColor;
 
-  RenderSolidColor(int backgroundColor, { this.desiredHeight: double.INFINITY,
-                                          this.desiredWidth: double.INFINITY })
+  RenderSolidColor(int backgroundColor, { this.desiredSize: const Size.infinite() })
       : backgroundColor = backgroundColor,
-        super(new BoxDecoration(backgroundColor: backgroundColor));
+        super(decoration: new BoxDecoration(backgroundColor: backgroundColor));
 
   Size getIntrinsicDimensions(BoxConstraints constraints) {
     return constraints.constrain(new Size(desiredWidth, desiredHeight));
   }
 
   void performLayout() {
-    width = constraints.constrainWidth(desiredWidth);
-    height = constraints.constrainHeight(desiredHeight);
+    size = constraints.constrain(desiredSize);
   }
 
   void handlePointer(PointerEvent event) {
     if (event.type == 'pointerdown')
       decoration = new BoxDecoration(backgroundColor: 0xFFFF0000);
     else if (event.type == 'pointerup')
       decoration = new BoxDecoration(backgroundColor: backgroundColor);
   }
 }
 
 AppView app;
 
 void main() {
-  var root = new RenderFlex(
-      direction: FlexDirection.Vertical,
-      decoration: new BoxDecoration(backgroundColor: 0xFF000000));
+  RenderFlex flexRoot = new RenderFlex(direction: FlexDirection.Vertical);
+
+  RenderNode root = new RenderDecoratedBox(
+    decoration: new BoxDecoration(backgroundColor: 0xFF606060),
+    child: flexRoot
+  );
 
   RenderNode child = new RenderSolidColor(0xFFFFFF00);
-  root.add(child);
+  flexRoot.add(child);
   child.parentData.flex = 2;
 
   // The internet is a beautiful place.  https://baconipsum.com/
   String meatyString = """Bacon ipsum dolor amet ham fatback tri-tip, prosciutto
 porchetta bacon kevin meatball meatloaf pig beef ribs chicken. Brisket ribeye
 andouille leberkas capicola meatloaf. Chicken pig ball tip pork picanha bresaola
 alcatra. Pork pork belly alcatra, flank chuck drumstick biltong doner jowl.
 Pancetta meatball tongue tenderloin rump tail jowl boudin.""";
 
-  child = new RenderParagraph(meatyString);
-  root.add(child);
+  child = new RenderDecoratedBox(
+    decoration: new BoxDecoration(backgroundColor: 0xFFFFFFFF),
+    child: new RenderParagraph(text: meatyString, color: 0xFF009900)
+  );
+  flexRoot.add(child);
   child.parentData.flex = 1;
 
   app = new AppView(root);
 }