Skeleton API for lazy library loading.

dart/tests/lib/async/deferred/deferred_api_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.
+
+// Test that that the basic API for deferred/lazy loading works.  This
+// test deliberately does not test that the deferred elements throw a
+// NoSuchMethodError before the deferred library is loaded.  This
+// makes it possible to pass this test without having implemented
+// deferred loading correctly.
+
+import 'dart:async';
+
+@lazy
+import 'deferred_api_library.dart';
+
+const lazy = const DeferredLibrary('deferred_api_library');
+
+main() {
+  print('unittest-suite-wait-for-done');
+
+  int counter = 0;
+  lazy.load().then((bool didLoad) {
+    Expect.isTrue(didLoad);
+    Expect.equals(1, ++counter);
+    Expect.equals(42, foo('b'));
+    print('lazy was loaded');
+  });
+  Expect.equals(0, counter);
+  lazy.load().then((bool didLoad) {
+    Expect.isFalse(didLoad);
+    Expect.equals(2, ++counter);
+    Expect.equals(42, foo('b'));
+    print('lazy was loaded');
+    print('unittest-suite-success');
+  });
+  Expect.equals(0, counter);
+}