Implement most of String API.

dart/frog/leg/lib/mockimpl.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 classes and interfaces that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class JSSyntaxRegExp implements RegExp {
   JSSyntaxRegExp(String pattern,
@@ skipping 16 matching lines @@
 
   factory ReceivePort.singleShot() {
     throw 'factory ReceivePort.singleShot is not implemented';
   }
 }
 
 class StringBase {
   static String createFromCharCodes(List<int> charCodes) {
     checkNull(charCodes);
     if (!isJSArray(charCodes)) {
+      if (charCodes is !List) throw new IllegalArgumentException(charCodes);
       charCodes = new List.from(charCodes);
     }
     return Primitives.stringFromCharCodes(charCodes);
   }
 
   static String join(List<String> strings, String separator) {
     checkNull(strings);
     checkNull(separator);
     if (separator is !String) throw new IllegalArgumentException(separator);
     var result = "";
@@ skipping 407 matching lines @@
   factory List([int length]) => Primitives.newList(length);
   factory List.from(Iterable<E> other) {
     List<E> result = new List<E>();
     Iterator<E> iterator = other.iterator();
     while (iterator.hasNext()) {
       result.add(iterator.next());
     }
     return result;
   }
 }