Migrate language/arithmetic2_test ... language/async_await_syntax_test.

tests/language_2/async_await_catch_regression_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 "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 foo() async {
   throw 42;
 }
 
 test() async {
   var exception;
   try {
     await foo();
   } catch (e) {
     print(await (e));
     await (exception = await e);
   }
   Expect.equals(42, exception);
 }
 
 main() {
   asyncStart();
   test().then((_) => asyncEnd());
 }