First step in eliminating —enable_async flag

tests/language/async_test.dart

 // Copyright (c) 2014, 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.
 
-// VMOptions=--enable_async
 
 import 'package:expect/expect.dart';
 
 import 'dart:async';
 
 topLevelFunction() async { }
 
 Future<int> topLevelWithParameter(int a) async {
   return 7 + a;
 }
@@ skipping 73 matching lines @@
   asyncReturn = a.getter;  /// type-mismatch4: static type warning, dynamic type error
   Expect.isTrue(asyncReturn is Future);  /// type-mismatch4: continued
   asyncReturn.then((int result) => Expect.equals(result, 18));  /// type-mismatch4: continued
 
   var b = new A(9);
   asyncReturn = a + b;
   Expect.isTrue(asyncReturn is Future);
   asyncReturn.then((A result) => Expect.equals(result.value, 22));
 
   var foo = 17;
-  bar(int p1, p2) async { 
+  bar(int p1, p2) async {
     var z = 8;
-    return p2 + z + foo; 
+    return p2 + z + foo;
   }
   asyncReturn = bar(1,2);
   Expect.isTrue(asyncReturn is Future);
   asyncReturn.then((int result) => Expect.equals(result, 27));
 
   var moreNesting = (int shadowP1, String p2, num p3) {
     var z = 3;
     aa(int shadowP1) async {
       return foo + z + p3 + shadowP1;
     }
     return aa(6);
   };
   asyncReturn = moreNesting(1, "ignore", 2);
   Expect.isTrue(asyncReturn is Future);
   asyncReturn.then((int result) => Expect.equals(result, 28));
 
   var b1 = const B.createConst(4);  /// constructor4: compile-time error
   var b2 = new B();
   b2.dontDoThat = 4;  /// setter1: compile-time error
 
   var checkAsync = (var someFunc) {
     var toTest = someFunc();
     Expect.isTrue(toTest is Future);
     toTest.then((int result) => Expect.equals(result, 4));
   };
   checkAsync(() async => 4);
 
 }