Fix int.parse bug (dart2js version)

sdk/lib/core/int.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.
 
 part of dart.core;
 
 /**
  * An arbitrarily large integer.
  *
  * **Note:** When compiling to JavaScript, integers are
@@ skipping 259 matching lines @@
    * optionally prefixed with a minus or plus sign ('-' or '+').
    *
    * It must always be the case for an int [:n:] and radix [:r:] that
    * [:n == int.parse(n.toRadixString(r), radix: r):].
    *
    * If the [source] is not a valid integer literal, optionally prefixed by a
    * sign, the [onError] is called with the [source] as argument, and its return
    * value is used instead. If no [onError] is provided, a [FormatException]
    * is thrown.
    *
+   * The [onError] handler can be chosen to return `null`.  This is preferable
+   * to to throwing and then immediately catching the [FormatException].
+   * Example:
+   *
+   *     var value = int.parse(text, onError: (source) => null);
+   *     if (value == null) ... handle the problem
+   *
    * The [onError] function is only invoked if [source] is a [String]. It is
    * not invoked if the [source] is, for example, `null`.
    */
   external static int parse(String source,
                             { int radix,
                               int onError(String source) });
 }