Make RuntimeError an Error

sdk/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.
 
 /**
  * A marker interface implemented by all core library exceptions.
  *
  * An [Exception] is intended to convey information to the user about a failure,
@@ skipping 46 matching lines @@
   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";
-}