Revert "Add List.first."

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;
 
 part 'ChangeEvent.dart';
 part 'EventBatch.dart';
 
 /**
@@ skipping 166 matching lines @@
       add(element);
     }
   }
 
   int push(T element) {
     recordListInsert(length, element);
     _internal.add(element);
     return _internal.length;
   }
 
-  T get first => _internal.first;
   T get last => _internal.last;
 
   T removeLast() {
     final result = _internal.removeLast();
     recordListRemove(length, result);
     return result;
   }
 
   T removeAt(int index) {
     int i = 0;
@@ skipping 88 matching lines @@
     // Only fire on an actual change.
     if (!identical(newValue, _value)) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }