Avoid spurious "The compiler crashed" messages in batch mode.

tests/compiler/dart2js/dart2js_batch2_run.dart

Index: tests/compiler/dart2js/dart2js_batch2_run.dart
diff --git a/runtime/lib/async_patch.dart b/tests/compiler/dart2js/dart2js_batch2_run.dart
similarity index 83%
copy from runtime/lib/async_patch.dart
copy to tests/compiler/dart2js/dart2js_batch2_run.dart
index 682ee8b10a4ec2d6b8496a5f06496f428819a00e..aee55ef18e5fa77c47bcbf53f5c16125299ed77a 100644
--- a/runtime/lib/async_patch.dart
+++ b/tests/compiler/dart2js/dart2js_batch2_run.dart
@@ -2,5 +2,9 @@
 // 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:_internal";
+@notExisting
+var x;
 
+main() {
+  print(x);
+}