Make 'where' lazy.

samples/swarm/DataSource.dart

Index: samples/swarm/DataSource.dart
diff --git a/samples/swarm/DataSource.dart b/samples/swarm/DataSource.dart
index 658e8a5c1aa2af0f6c26718411238eae7f4a035d..8bb316cc6cba931e682bd5952572f5c5cc52a4ef 100644
--- a/samples/swarm/DataSource.dart
+++ b/samples/swarm/DataSource.dart
@@ -87,9 +87,6 @@ class Sections extends Collection<Section> {
   List<Section> get sections => _sections;
 
   // Collection<Section> methods:
-  List<Section> where(bool f(Section element)) {
-    return Collections.where(this, new List<Section>(), f);
-  }
   bool every(bool f(Section element)) => Collections.every(this, f);
   bool some(bool f(Section element)) => Collections.some(this, f);
   void forEach(void f(Section element)) { Collections.forEach(this, f); }