Rename runAsync to scheduleMicrotask.

tests/lib/async/zone_run_guarded_test.dart

 // Copyright (c) 2013, 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';
 import 'dart:async';
 
 main() {
   Completer done = new Completer();
@@ skipping 39 matching lines @@
   Expect.listEquals(
       [ "forked.run", "runGuarded 1", "after runGuarded 1",
         "forked.run", "runGuarded 2", "forked.handleUncaught 42" ],
       events);
 
   events.clear();
   asyncStart();
   result = forked.runGuarded(() {
     Expect.identical(forked, Zone.current);
     events.add("run closure");
-    runAsync(() {
+    scheduleMicrotask(() {
       events.add("run closure 2");
       Expect.identical(forked, Zone.current);
       done.complete(true);
       throw 88;
     });
     throw 1234;
   });
-  events.add("after nested runAsync");
+  events.add("after nested scheduleMicrotask");
   Expect.equals(499, result);
 
   done.future.whenComplete(() {
     Expect.listEquals(
         ["forked.run", "run closure", "forked.handleUncaught 1234",
-         "after nested runAsync", "forked.run", "run closure 2",
+         "after nested scheduleMicrotask", "forked.run", "run closure 2",
          "forked.handleUncaught 88" ],
         events);
     asyncEnd();
   });
 }