Fix int.parse bug (dart2js version)

sdk/lib/core/int.dart

Index: sdk/lib/core/int.dart
diff --git a/sdk/lib/core/int.dart b/sdk/lib/core/int.dart
index 681b8e8815a4f0f166fbc22c51cf92de08d781a9..1d29a728f0399e2c16059fa1bb0ec26b69d29c8b 100644
--- a/sdk/lib/core/int.dart
+++ b/sdk/lib/core/int.dart
@@ -277,6 +277,13 @@ abstract class int extends num {
    * 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`.
    */