Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/tests/vm/dart/isolate_unhandled_exception_uri_helper.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.
 
 library isolate_unhandled_exception_uri_helper;
 
 import 'dart:isolate';
 
 // Isolate script that throws an uncaught exception, which is caught by an
 // uncaught exception handler.
 
 void main() {
   port.receive((message, replyTo) {
     if (message == 'throw exception') {
       replyTo.call('throwing exception');
-      throw new RuntimeError('ignore this exception');
+      throw new UnsupportedError('ignore this exception');
     }
     replyTo.call('hello');
     port.close();
   });
 }
 
 bool _unhandledExceptionCallback(IsolateUnhandledException e) {
   return e.source.message == 'ignore this exception';
 }