Add a test for the sector app.

sky/examples/widgets/sector.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 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/theme2/colors.dart';
 import 'package:sky/theme2/edges.dart';
@@ skipping 10 matching lines @@
 RenderBox initCircle() {
   return new RenderBoxToRenderSectorAdapter(
     innerRadius: 25.0,
     child: new RenderSectorRing(padding: 0.0)
   );
 }
 
 class SectorApp extends App {
 
   RenderBoxToRenderSectorAdapter sectors = initCircle();
-  math.Random rand = new math.Random();
+  math.Random rand = new math.Random(1);
 
   void addSector() {
     double deltaTheta;
     var ring = (sectors.child as RenderSectorRing);
     SectorDimensions currentSize = ring.getIntrinsicDimensions(const SectorConstraints(), ring.deltaRadius);
     if (currentSize.deltaTheta >= kTwoPi - (math.PI * 0.2 + 0.05))
       deltaTheta = kTwoPi - currentSize.deltaTheta;
     else
       deltaTheta = math.PI * rand.nextDouble() / 5.0 + 0.05;
     Color color = new Color(((0xFF << 24) + rand.nextInt(0xFFFFFF)) | 0x808080);
@@ skipping 92 matching lines @@
   }
 }
 
 void main() {
   runApp(new SectorApp());
   WidgetAppView.appView.onFrame = () {
     // uncomment this for debugging:
     // WidgetAppView.appView.debugDumpRenderTree();
   };
 }