Change NotImplementedException to UnimplementedError.

lib/core/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.
  * Defaults to an implementation that only carries a simple message.
  */
@@ skipping 43 matching lines @@
     }
   }
 
   String get exceptionName => "NullPointerException";
 
   final String functionName;
   final List arguments;
 }
 
 
-class NotImplementedException implements Exception {
-  const NotImplementedException([String message]) : this._message = message;
-  String toString() => (this._message !== null
-                        ? "NotImplementedException: $_message"
-                        : "NotImplementedException");
-  final String _message;
-}
-
-
 class IllegalJSRegExpException implements Exception {
   const IllegalJSRegExpException(String this._pattern, String this._errmsg);
   String toString() => "IllegalJSRegExpException: '$_pattern' '$_errmsg'";
   final String _pattern;
   final String _errmsg;
 }
 
 
 class IntegerDivisionByZeroException implements Exception {
   const IntegerDivisionByZeroException();
   String toString() => "IntegerDivisionByZeroException";
 }
 
 /**
  * Exception thrown when a runtime error occurs.
  */
 class RuntimeError implements Exception {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }