Document the exception on DateFormat.parse

pkg/intl/lib/date_format.dart

Index: pkg/intl/lib/date_format.dart
diff --git a/pkg/intl/lib/date_format.dart b/pkg/intl/lib/date_format.dart
index 202ae1b4cb83957f287566a4225ade55731e02cb..17aca41199e22f7fe940c27c278d5f465cbf76bd 100644
--- a/pkg/intl/lib/date_format.dart
+++ b/pkg/intl/lib/date_format.dart
@@ -252,7 +252,8 @@ class DateFormat {
 
   /**
    * Given user input, attempt to parse the [inputString] into the anticipated
-   * format, treating it as being in the local timezone.
+   * format, treating it as being in the local timezone. If [inputString] does
+   * not match our format, throws a [FormatException].
    */
   DateTime parse(String inputString, [utc = false]) {
     // TODO(alanknight): The Closure code refers to special parsing of numeric