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

sky/examples/raw/sector_layout.dart

Index: sky/examples/raw/sector_layout.dart
diff --git a/sky/examples/raw/sector_layout.dart b/sky/examples/raw/sector_layout.dart
index 605009ac91780196efa864b6f6ea8de276f47e88..2b1d6a0c90af77ccd83b37c6f8a8a588c6d552e0 100644
--- a/sky/examples/raw/sector_layout.dart
+++ b/sky/examples/raw/sector_layout.dart
@@ -71,7 +71,7 @@ abstract class RenderSector extends RenderObject {
     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);