Big merge from experimental to bleeding edge.

samples/clock/balls.dart

Index: samples/clock/balls.dart
diff --git a/samples/clock/balls.dart b/samples/clock/balls.dart
index d9816f00d5a9d3872c2ea8575551a16cd25d04da..d497c6dcd2cf1730e1e44d395e48225367bf2efd 100644
--- a/samples/clock/balls.dart
+++ b/samples/clock/balls.dart
@@ -46,7 +46,7 @@ class Balls {
     lastTime = now;
 
     // incrementally move each ball, removing balls that are offscreen
-    balls = balls.filter((ball) => ball.tick(delta));
+    balls = balls.where((ball) => ball.tick(delta)).toList();
     collideBalls(delta);
   }