Add a simple inksplash example

sky/examples/raw/touch_demo.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';
 import 'dart:sky';
 import 'package:sky/framework/app.dart';
 import 'package:sky/framework/rendering/render_box.dart';
 import 'package:sky/framework/rendering/render_node.dart';
 
@@ skipping 43 matching lines @@
       case 'pointercancel':
         dots = new Map();
         break;
       case 'pointermove':
         dots[event.pointer].update(event);
         break;
     }
     markNeedsPaint();
   }
 
+  void performLayout() {
+    size = constraints.constrain(new Size.infinite());
+  }
+
   void paint(RenderNodeDisplayList canvas) {
     dots.forEach((_, Dot dot) {
       dot.paint(canvas);
     });
   }
 }
 
 AppView app;
 
 void main() {
   app = new AppView(new RenderTouchDemo());
 }