Add version validation for LookupMap, also add unittest directly in LookupMap (take 2)

pkg/lookup_map/lib/lookup_map.dart

 // Copyright (c) 2015, 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.
 
 /// Defines [LookupMap], a simple map that can be optimized by dart2js.
 library lookup_map;
 
 /// [LookupMap] is a simple, but very restricted map.  The map can only hold
 /// constant keys and the only way to use the map is to retrieve values with a
 /// key you already have.  Expect for lookup, any other operation in [Map] (like
@@ skipping 73 matching lines @@
     for (var i = 0; i < _entries.length; i += 2) {
       map[_entries[i]] = _entries[i + 1];
     }
     if (_key != null) map[_key] = _value;
   }
 }
 
 /// An expando that stores a flatten version of a [LookupMap], this is
 /// computed and stored the first time the map is accessed.
 final _flatMap = new Expando('_flat_map');
+
+/// Internal constant that matches the version in the pubspec. This is used by
+/// dart2js to ensure that optimizations are only enabled on known versions of
+/// this code.
+// Note: this needs to be kept in sync with the pubspec, otherwise
+// test/version_check_test would fail.
+final _version = '0.0.1';