Update unwrapException to give better exceptions on Firefox.

corelib/src/exceptions.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.
 
 // Exceptions are thrown either by the VM or from Dart code.
 
 /**
  * Interface implemented by all core library exceptions.
  */
 interface Exception default ExceptionImplementation {
@@ skipping 113 matching lines @@
   const NullPointerException([this.functionName, this.arguments = const []]);
   String toString() {
     if (functionName == null) {
       return exceptionName;
     } else {
       return "$exceptionName : method: '$functionName'\n"
           "Receiver: null\n"
           "Arguments: $arguments";
     }
   }
-  
+
   String get exceptionName() => "NullPointerException";
 
   final String functionName;
   final List arguments;
 }
 
 
 class NoMoreElementsException implements Exception {
   const NoMoreElementsException();
   String toString() => "NoMoreElementsException";
@@ skipping 24 matching lines @@
   String toString() => "IllegalJSRegExpException: '$_pattern' '$_errmsg'";
   final String _pattern;
   final String _errmsg;
 }
 
 
 class IntegerDivisionByZeroException implements Exception {
   const IntegerDivisionByZeroException();
   String toString() => "IntegerDivisionByZeroException";
 }