Port the remaining of dart:coreimpl to the unified corelib.

lib/compiler/implementation/lib/mock.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.
 
 // Mocks of things that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class AssertionError {}
 class TypeError extends AssertionError {
@@ skipping 46 matching lines @@
   factory Uint8List(int length) {
     throw new UnsupportedOperationException("new Uint8List($length)");
   }
 }
 
 // TODO(ahe): This definitely does not belong in the core library.
 void exit(int exitCode) {
   throw new UnsupportedOperationException("exit($exitCode)");
 }
 
-class _Expando<T> implements Expando<T> {
-
-  final String name;
-
-  const _Expando([this.name]);
-
-  T operator[](Object object) {
-    var values = Primitives.getProperty(object, EXPANDO_PROPERTY_NAME);
-    return (values === null) ? null : Primitives.getProperty(values, _getKey());
-  }
-
-  void operator[]=(Object object, T value) {
-    var values = Primitives.getProperty(object, EXPANDO_PROPERTY_NAME);
-    if (values === null) {
-      values = new Object();
-      Primitives.setProperty(object, EXPANDO_PROPERTY_NAME, values);
-    }
-    Primitives.setProperty(values, _getKey(), value);
-  }
-
-  String toString() {
-    String key = _getKey();
-    return (name === null) ? "Expando:${key}" : "Expando:${name}@${key}";
-  }
-
-  String _getKey() {
-    String key = Primitives.getProperty(this, KEY_PROPERTY_NAME);
-    if (key === null) {
-      key = "expando\$key\$${keyCount++}";
-      Primitives.setProperty(this, KEY_PROPERTY_NAME, key);
-    }
-    return key;
-  }
-
-  static final String KEY_PROPERTY_NAME = 'expando\$key';
-  static final String EXPANDO_PROPERTY_NAME = 'expando\$values';
-  static int keyCount = 0;
-
-}