Convert String to a class.

lib/coreimpl/string.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.
-
-class StringImplementation {
-  /**
-   * Factory implementation of String.fromCharCodes:
-   * Allocates a new String for the specified [charCodes].
-   */
-  factory String.fromCharCodes(List<int> charCodes) {
-    return _fromCharCodes(charCodes);
-  }
-
-  external static String _fromCharCodes(List<int> charCodes);
-
-  /**
-   * Joins all the given strings to create a new string.
-   */
-  external static String join(List<String> strings, String separator);
-
-  /**
-   * Concatenates all the given strings to create a new string.
-   */
-  external static String concatAll(List<String> strings);
-
-}