Fix test to not reach out of current dir

tests/corelib/string_operations_with_null_test.dart

Index: tests/corelib/string_operations_with_null_test.dart
diff --git a/tests/corelib/string_operations_with_null_test.dart b/tests/corelib/string_operations_with_null_test.dart
index 7288001d4941f4b31c74f684945fe2d37fbd5dc0..cac0c7ced0f32cd8422d65f7c523ffdb51201d8f 100644
--- a/tests/corelib/string_operations_with_null_test.dart
+++ b/tests/corelib/string_operations_with_null_test.dart
@@ -3,11 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
-import "../language/compiler_annotations.dart";
 
-@DontInline()
+@NoInline()
+@AssumeDynamic()
 returnStringOrNull() {
-  () => 42;
   return new DateTime.now().millisecondsSinceEpoch == 0 ? 'foo' : null;
 }