Remove cancel and make crash exit with code 253.

tests/compiler/dart2js/mock_compiler.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 mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:collection';
 
@@ skipping 426 matching lines @@
     // Do nothing. The mock core library is already handled in the constructor.
     return new Future.value();
   }
 
   Uri translateResolvedUri(LibraryElement importingLibrary,
                            Uri resolvedUri, Node node) => resolvedUri;
 
   // The mock library doesn't need any patches.
   Uri resolvePatchUri(String dartLibraryName) => null;
 
-  Future<Script> readScript(Uri uri, [Element element, Node node]) {
+  Future<Script> readScript(Spannable node, Uri uri) {
     SourceFile sourceFile = sourceFiles[uri.toString()];
     if (sourceFile == null) throw new ArgumentError(uri);
     return new Future.value(new Script(uri, uri, sourceFile));
   }
 
   Element lookupElementIn(ScopeContainerElement container, name) {
     Element element = container.localLookup(name);
     return element != null
         ? element
         : new ErroneousElementX(null, null, name, container);
@@ skipping 117 matching lines @@
     } else {
       sourceFile = compiler.sourceFiles[uri.toString()];
     }
     if (sourceFile != null && begin != null && end != null) {
       print(sourceFile.getLocationMessage(message, begin, end, true, (x) => x));
     } else {
       print(message);
     }
   };
 }