Correctly compile unresolved for-in loops.

dart/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:collection';
 import 'dart:uri';
 
@@ skipping 218 matching lines @@
     var script = new Script(uri, new MockFile(source));
     var library = new LibraryElementX(script);
     parseScript(source, library);
     library.setExports(library.localScope.values.toList());
     registerSource(uri, source);
     libraries.putIfAbsent(uri.toString(), () => library);
     return library;
   }
 
   void reportWarning(Node node, var message) {
-    warnings.add(new WarningMessage(node, message.message));
+    if (message is! Message) message = message.message;
+    warnings.add(new WarningMessage(node, message));
   }
 
   void reportError(Node node, var message) {
     if (message is String && message.startsWith("no library name found in")) {
       // TODO(ahe): Fix the MockCompiler to not have this problem.
       return;
     }
-    errors.add(new WarningMessage(node, message.message));
+    if (message is! Message) message = message.message;
+    errors.add(new WarningMessage(node, message));
   }
 
   void reportMessage(SourceSpan span, var message, api.Diagnostic kind) {
     var diagnostic = new WarningMessage(null, message.message);
     if (kind == api.Diagnostic.ERROR) {
       errors.add(diagnostic);
     } else {
       warnings.add(diagnostic);
     }
   }
@@ skipping 130 matching lines @@
   }
 }
 
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   void registerMainApp(LibraryElement mainApp) {
     // Do nothing.
   }
 }