Fix error message for library name mismatch.

tests/compiler/dart2js/part_of_test.dart

+// Copyright (c) 2013, 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 part_of_test;
+
+import 'dart:uri';
+import 'mock_compiler.dart';
+import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
+    show MessageKind;
+
+final libraryUri = new Uri('test:library.dart');
+const String LIBRARY_SOURCE = '''
+library foo;
+part 'part.dart';
+''';
+
+final partUri = new Uri('test:part.dart');
+const String PART_SOURCE = '''
+part of bar;
+''';
+
+void main() {
+  var compiler = new MockCompiler();
+  compiler.registerSource(libraryUri, LIBRARY_SOURCE);
+  compiler.registerSource(partUri, PART_SOURCE);
+
+  compiler.libraryLoader.loadLibrary(libraryUri, null, libraryUri);
+  print('errors: ${compiler.errors}');
+  print('warnings: ${compiler.warnings}');
+  Expect.isTrue(compiler.errors.isEmpty);
+  Expect.equals(1, compiler.warnings.length);
+  Expect.equals(MessageKind.LIBRARY_NAME_MISMATCH,
+                compiler.warnings[0].message.kind);
+  Expect.equals("${MessageKind.LIBRARY_NAME_MISMATCH.error(['foo'])}",
+                compiler.warnings[0].message.toString());
+}