Add expectAsyncX and expectAsyncUntilX methods, and deprecate the old methods.

test/runner/signal_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.
 
 // Windows doesn't support sending signals.
 @TestOn("vm && !windows")
 
 import 'dart:async';
 import 'dart:io';
 
@@ skipping 216 matching lines @@
 
   tearDown(() {
     new File("output").writeAsStringSync(expectAsyncThrewError.toString());
   });
 
   test("test", () async {
     print("running test");
 
     await new Future.delayed(new Duration(seconds: 1));
     try {
-      expectAsync(() {});
+      expectAsync0(() {});
     } catch (_) {
       expectAsyncThrewError = true;
     }
   });
 }
 """).create();
 
       var test = _runTest(["test.dart"]);
       test.stdout.expect(consumeThrough("running test"));
       signalAndQuit(test);
@@ skipping 11 matching lines @@
 
 void signalAndQuit(ScheduledProcess test) {
   test.signal(ProcessSignal.SIGTERM);
   test.shouldExit();
   test.stderr.expect(isDone);
 }
 
 void expectTempDirEmpty() {
   schedule(() => expect(new Directory(_tempDir).listSync(), isEmpty));
 }