Replace some 'as' operators with equivalent code that doesn't do any checks in production mode.

sky/examples/raw/sector_layout.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 'package:sky/framework/app.dart';
 import 'package:sky/framework/rendering/box.dart';
 import 'package:sky/framework/rendering/object.dart';
 
@@ skipping 53 matching lines @@
 
   void setParentData(RenderObject child) {
     if (child.parentData is! SectorParentData)
       child.parentData = new SectorParentData();
   }
 
   SectorDimensions getIntrinsicDimensions(SectorConstraints constraints, double radius) {
     return new SectorDimensions.withConstraints(constraints);
   }
 
-  SectorConstraints get constraints => super.constraints as SectorConstraints;
+  SectorConstraints get constraints { SectorConstraints result = super.constraints; return result; }
   void performResize() {
     // default behaviour for subclasses that have sizedByParent = true
     deltaRadius = constraints.constrainDeltaRadius(0.0);
     deltaTheta = constraints.constrainDeltaTheta(0.0);
   }
   void performLayout() {
     // descendants have to either override performLayout() to set both
     // the dimensions and lay out children, or, set sizedByParent to
     // true so that performResize()'s logic above does its thing.
     assert(sizedByParent);
@@ skipping 412 matching lines @@
   rootCircle.add(new RenderSolidColor(const Color(0xFF0000FF), desiredDeltaTheta: kTwoPi * 0.4));
   var stack = new RenderSectorSlice(padding: 2.0);
   stack.add(new RenderSolidColor(const Color(0xFFFFFF00), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFFFF9000), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFF00FF00)));
   rootCircle.add(stack);
 
   var root = new RenderBoxToRenderSectorAdapter(innerRadius: 50.0, child: rootCircle);
   app = new AppView(root);
 }