Implement LibraryMirror.metadata.

dart/tests/lib/mirrors/metadata_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.
+
+@fisk @symbol
+library test.metadata_test;
+
+import 'dart:mirrors';
+
+const fisk = 'a metadata string';
+
+const symbol = const Symbol('fisk');
+
+main() {
+  MirrorSystem mirrors = currentMirrorSystem();
+  LibraryMirror library =
+      mirrors.findLibrary(const Symbol('test.metadata_test')).first;
+  List metadata = library.metadata.map((m) => m.reflectee).toList();
+  if (metadata.length != 2) {
+    throw 'Expected two pieces of metadata on library';
+  }
+  if (!metadata.contains(fisk)) {
+    throw '$metadata does not contain "$fisk"';
+  }
+  if (!metadata.contains(symbol)) {
+    throw '$metadata does not contain "$symbol"';
+  }
+  if (MirrorSystem.getName(symbol) != 'fisk') {
+    // This happened in dart2js due to how early library metadata is
+    // computed.
+    throw 'Bad constant: $symbol';
+  }
+  print(metadata);
+}