Remove cancel and make crash exit with code 253.

sdk/lib/_internal/compiler/implementation/warnings.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 dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 785 matching lines @@
 """]);
 
   static const MessageKind DUPLICATE_EXTENDS_IMPLEMENTS = const MessageKind(
       "'#{type}' can not be both extended and implemented.");
 
   static const MessageKind DUPLICATE_IMPLEMENTS = const MessageKind(
       "'#{type}' must not occur more than once "
       "in the implements clause.");
 
   static const MessageKind MULTI_INHERITANCE = const MessageKind(
-      "Inheritance of the same class with different type "
-      "arguments is not supported: Both #{firstType} and #{secondType} are "
+      "Dart2js does not currently support inheritance of the same class with "
+      "different type arguments: Both #{firstType} and #{secondType} are "
       "supertypes of #{thisType}.");
 
   static const MessageKind ILLEGAL_SUPER_SEND = const MessageKind(
       "'#{name}' cannot be called on super.");
 
   static const MessageKind NO_SUCH_SUPER_MEMBER = const MessageKind(
       "Cannot resolve '#{memberName}' in a superclass of '#{className}'.");
 
   static const MessageKind ADDITIONAL_TYPE_ARGUMENT = const MessageKind(
       "Additional type argument.");
@@ skipping 400 matching lines @@
       "'_'.");
 
   static const MessageKind PRIVATE_NAMED_PARAMETER = const MessageKind(
       "Named optional parameter can't have a library private name.",
       howToFix: "Try removing the '_' or making the parameter positional or "
         "required.",
       examples: const ["""foo({int _p}) {} main() => foo();"""]
       );
 
   static const MessageKind UNSUPPORTED_LITERAL_SYMBOL = const MessageKind(
-      "Symbol literal '##{value}' is currently unsupported.");
+      "Symbol literal '##{value}' is currently unsupported by dart2js.");
 
   static const MessageKind INVALID_SYMBOL = const MessageKind('''
 '#{value}' is not a valid Symbol name because is not:
  * an empty String,
  * a user defined operator,
  * a qualified non-private identifier optionally followed by '=', or
  * a qualified non-private identifier followed by '.' and a user-defined '''
 "operator.");
 
   static const MessageKind AMBIGUOUS_REEXPORT = const MessageKind(
@@ skipping 684 matching lines @@
     return computeMessage();
   }
 
   bool operator==(other) {
     if (other is !Message) return false;
     return (kind == other.kind) && (toString() == other.toString());
   }
 
   int get hashCode => throw new UnsupportedError('Message.hashCode');
 }