Make 'where' lazy.

samples/swarm/DataSource.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /** The top-level collection of all sections for a user. */
 // TODO(jimhug): This is known as UserData in the server model.
 class Sections extends Collection<Section> {
   final List<Section> _sections;
 
   Sections(this._sections);
@@ skipping 69 matching lines @@
       if (name == _sections[i].title) {
         return i;
       }
     }
     return -1;
   }
 
   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); }
 
   // TODO(jmesserly): this should be a property
   bool get isEmpty => length == 0;
 }
 
 
 /** A collection of data sources representing a page in the UI. */
@@ skipping 132 matching lines @@
     final hasThumbnail = decoder.readBool();
     final author = decoder.readString();
     final dateInSeconds = decoder.readInt();
     final snippet = decoder.readString();
     final date =
         new Date.fromMillisecondsSinceEpoch(dateInSeconds*1000, isUtc: true);
     return new Article(source, id, date, title, author, srcUrl, hasThumbnail,
         snippet);
   }
 }