Create an outline of metadata API in dart2js.

dart/tests/compiler/dart2js/metadata_test.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.
+
+#import("dart:uri");
+
+#import('compiler_helper.dart');
+
+#import('../../../lib/compiler/implementation/elements/elements.dart');
+#import('../../../lib/compiler/implementation/leg.dart');
+
+void testClassMetadata() {
+  // TODO(ahe): native should be "const", not "final".
+  final source = """final native = 'xyz';
+                    @native class Foo {}
+                    main() {}""";
+
+  check(compiler, element) {
+    return; // TODO(ahe): I'm working on the following.
+    Expect.isFalse(element.metadata.isEmpty());
+    MetadataAnnotation annotation = element.metadata.head;
+    Expect.isNotNull(annotation);
+    Constant value = annotation.value;
+    print(value);
+  }
+
+  compileAndCheck(source, 'Foo', check);
+}
+
+void main() {
+  testClassMetadata();
+}