Add extra information to FormatException.

sdk/lib/core/date_time.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.
 
 part of dart.core;
 
 /**
  * An instant in time, such as July 20, 1969, 8:18pm GMT.
  *
  * Create a DateTime object by using one of the constructors
@@ skipping 264 matching lines @@
           int sign = (match[9] == '-') ? -1 : 1;
           int hourDifference = int.parse(match[10]);
           int minuteDifference = parseIntOrZero(match[11]);
           minuteDifference += 60 * hourDifference;
           minute -= sign * minuteDifference;
         }
       }
       int millisecondsSinceEpoch = _brokenDownDateToMillisecondsSinceEpoch(
           years, month, day, hour, minute, second, millisecond, isUtc);
       if (millisecondsSinceEpoch == null) {
-        throw new FormatException(formattedString);
+        throw new FormatException("Time out of range", formattedString);
       }
       if (addOneMillisecond) millisecondsSinceEpoch++;
       return new DateTime.fromMillisecondsSinceEpoch(millisecondsSinceEpoch,
                                                      isUtc: isUtc);
     } else {
-      throw new FormatException(formattedString);
+      throw new FormatException("Invalid date format", formattedString);
     }
   }
 
   static const int _MAX_MILLISECONDS_SINCE_EPOCH = 8640000000000000;
 
   /**
    * Constructs a new [DateTime] instance
    * with the given [millisecondsSinceEpoch].
    *
    * If [isUtc] is false then the date is in the local time zone.
@@ skipping 320 matching lines @@
    * In accordance with ISO 8601
    * a week starts with Monday, which has the value 1.
    *
    *     DateTime moonLanding = DateTime.parse("1969-07-20 20:18:00");
    *     assert(moonLanding.weekday == 7);
    *     assert(moonLanding.weekday == DateTime.SUNDAY);
    *
    */
   external int get weekday;
 }