unfork DDC's copy of most SDK libraries

pkg/dev_compiler/tool/input_sdk/lib/core/null.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.
-
-part of dart.core;
-
-/**
- * The reserved word [:null:] denotes an object that is the sole instance of 
- * this class.
- * 
- * It is a compile-time error for a class to attempt to extend or implement
- * Null.
- */
-class Null {
-  factory Null._uninstantiable() {
-    throw new UnsupportedError('class Null cannot be instantiated');
-  }
-
-  /** Returns the string `"null"`. */
-  String toString() => "null";
-}