Add List.insert.

samples/swarm/swarm_ui_lib/observable/observable.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.
 
 library observable;
 
 import 'dart:collection';
 
 part 'ChangeEvent.dart';
 part 'EventBatch.dart';
@@ skipping 180 matching lines @@
     return _internal.length;
   }
 
   T get first => _internal.first;
   T get last => _internal.last;
   T get single => _internal.single;
 
   T min([int compare(T a, T b)]) => _internal.min(compare);
   T max([int compare(T a, T b)]) => _internal.max(compare);
 
+  void insert(int index, T element) {
+    _internal.insert(index, element);
+    recordListInsert(index, element);
+  }
+
   T removeLast() {
     final result = _internal.removeLast();
     recordListRemove(length, result);
     return result;
   }
 
   T removeAt(int index) {
     T result = _internal.removeAt(index);
     recordListRemove(index, result);
     return result;
@@ skipping 119 matching lines @@
     // Only fire on an actual change.
     if (!identical(newValue, _value)) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }