Fix service test script to avoid unhandled exception.

runtime/observatory/tests/service/regress_28443_test.dart

Index: runtime/observatory/tests/service/regress_28443_test.dart
diff --git a/runtime/observatory/tests/service/regress_28443_test.dart b/runtime/observatory/tests/service/regress_28443_test.dart
index 09ffa798eea569cec9133a35c4cdb71698f0a69c..b135a6ffba62ff5aa20312188bf215ab4d768b3c 100644
--- a/runtime/observatory/tests/service/regress_28443_test.dart
+++ b/runtime/observatory/tests/service/regress_28443_test.dart
@@ -31,7 +31,11 @@ collect() async {
 }
 
 test_code() async {  // LINE_B
-  await collect();
+  try {
+    await collect();
+  } on TimeoutException {
+    print("ok");
+  }
 }
 
 Future<Isolate> stepThroughProgram(Isolate isolate) async {