Skeleton API for lazy library loading.

dart/runtime/lib/deferred_load_patch.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.
+
+final Set<String> _loadedLibraries = new Set<String>();
+
+patch class DeferredLibrary {
+  /* patch */ Future<bool> load() {
+    // Dummy implementation that should eventually be replaced by real
+    // implementation.
+    Future future =
+        new Future<bool>.immediate(!_loadedLibraries.contains(libraryName));
+    _loadedLibraries.add(libraryName);
+    return future;
+  }
+}