Make mappedBy lazy.

samples/swarm/swarm_ui_lib/util/CollectionUtils.dart

Index: samples/swarm/swarm_ui_lib/util/CollectionUtils.dart
diff --git a/samples/swarm/swarm_ui_lib/util/CollectionUtils.dart b/samples/swarm/swarm_ui_lib/util/CollectionUtils.dart
index ca515b10b3fce49c602eb4981442db2ea98fa307..fd4e2394a4061cb95ad31f54251c88bfe5ae445e 100644
--- a/samples/swarm/swarm_ui_lib/util/CollectionUtils.dart
+++ b/samples/swarm/swarm_ui_lib/util/CollectionUtils.dart
@@ -38,22 +38,6 @@ class CollectionUtils {
     }
   }
 
-  // Collection<T> supports most of the ES 5 list methods, but it's missing
-  // map.
-
-  // TODO(jmesserly): we might want a version of this that return an iterable,
-  // however JS, Python and Ruby versions are all eager.
-  static List mappedBy(Iterable source, var mapper) {
-    // TODO(jmesserly): I was trying to set the capacity here, but instead it
-    // seems to create a fixed list. Hence assigning by index below.
-    List result = new List(source is List ? (source as List).length : null);
-    int i = 0;
-    for (final item in source) {
-      result[i++] = mapper(item);
-    }
-    return result;
-  }
-
   /**
    * Finds the item in [source] that matches [test].  Returns null if
    * no item matches.  The typing should be: