Copy dart2js source into pkg/compiler

pkg/compiler/lib/src/scanner/keyword.dart

 // Copyright (c) 2011, 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 scanner;
 
 /**
  * A keyword in the Dart programming language.
  */
 class Keyword {
@@ skipping 185 matching lines @@
 /**
  * A state that has no outgoing transitions.
  */
 class LeafKeywordState extends KeywordState {
   LeafKeywordState(String syntax) : super(Keyword.keywords[syntax]);
 
   KeywordState next(int c) => null;
 
   String toString() => keyword.syntax;
 }