Revert "Parts must start with 'part of'" and "Attempt to fix VM build"

dart/lib/compiler/implementation/lib/constant_map.dart

 // Copyright (c) 2012, 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.
 
-part of js_helper;
-
 // This class has no constructor. This is on purpose since the instantiation
 // is shortcut by the compiler.
 class ConstantMap<V> implements Map<String, V> {
   final int length;
   // A constant map is backed by a JavaScript object.
   final _jsObject;
   final List<String> _keys;
 
   bool containsValue(V needle) {
     return getValues().some((V value) => value == needle);
@@ skipping 42 matching lines @@
   bool containsKey(String key) {
     if (key == '__proto__') return true;
     return super.containsKey(key);
   }
 
   V operator [](String key) {
     if (key == '__proto__') return _protoValue;
     return super[key];
   }
 }