Use annotations on confuse() in null_test

tests/language/null_test.dart

Index: tests/language/null_test.dart
diff --git a/tests/language/null_test.dart b/tests/language/null_test.dart
index 83ffd7b3d1b02f56293f7913b14ef7cd259fdda3..ecb2e002d690ebac37cf50b5a8cb044b15ec5b37 100644
--- a/tests/language/null_test.dart
+++ b/tests/language/null_test.dart
@@ -36,13 +36,9 @@ class Generic2<T, S> {
 // Magic incantation to avoid the compiler recognizing the constant values
 // at compile time. If the result is computed at compile time, the dynamic code
 // will not be tested.
-confuse(x) {
-  try {
-    if (new DateTime.now().millisecondsSinceEpoch == 42) x = 42;
-    throw [x];
-  } on dynamic catch (e) { return e[0]; }
-  return 42;
-}
+@NoInline()
+@AssumeDynamic()
+confuse(x) => x;
 
 void main() {
   for (int i = 0; i < 10; i++) {