Futures.wait should call then, even if some(or all) of the futures are done

tests/corelib/src/FuturesTest.dart

+// Copyright (c) 2011, 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.
+
+Future testWaitEmpty() {
+  List<Future> futures = new List<Future>();
+  return Futures.wait(futures);
+}
+
+Future testCompleteAfterWait() {
+  List<Future> futures = new List<Future>();
+  Completer<Object> c = new Completer<Object>();
+  futures.add(c.future);
+  Future future = Futures.wait(futures);
+  c.complete(null);
+  return future;
+}
+
+Future testCompleteBeforeWait() {
+  List<Future> futures = new List<Future>();
+  Completer c = new Completer();
+  futures.add(c.future);
+  c.complete(null);
+  return Futures.wait(futures);
+}
+
+main() {
+  List<Future> futures = new List<Future>();
+
+  futures.add(testWaitEmpty());
+  futures.add(testCompleteAfterWait());
+  futures.add(testCompleteBeforeWait());
+
+  // Use a receive port for blocking the test. 
+  // Note that if the test fails, the program will not end.
+  ReceivePort port = new ReceivePort();
+  Futures.wait(futures).then((List list) {
+    Expect.equals(3, list.length);
+    port.close();
+  });
+}