Reorganize mdv and observe packages

pkg/observe/test/observable_map_test.dart

 // Copyright (c) 2013, 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.
 
-import 'package:mdv_observe/mdv_observe.dart';
+import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'utils.dart';
 
 main() {
   // TODO(jmesserly): need all standard Map API tests.
 
   group('observe length', () {
     ObservableMap map;
     List<ChangeRecord> changes;
 
@@ skipping 216 matching lines @@
   });
 }
 
 
 const _LENGTH = const Symbol('length');
 
 final _lengthChange = new PropertyChangeRecord(_LENGTH);
 
 _change(key, {isInsert: false, isRemove: false}) =>
     new MapChangeRecord(key, isInsert: isInsert, isRemove: isRemove);