Fix more async machinery (issue 22579 and possibly more to be triaged).

tests/language/regress_22579_test.dart

+// Copyright (c) 2015, 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:async";
+import "package:expect/expect.dart";
+
+foo() async {
+  try {
+    await 1;
+  } catch(e) {
+  }
+  throw "error";
+}
+
+main() async {
+  var error = "no error";
+  try {
+    await foo();
+  } catch (e) {
+    error = e;
+  }
+  Expect.equals("error", error);
+}
+