Address observatory analysis issues.

runtime/observatory/tests/service/async_single_step_exception_test.dart

Index: runtime/observatory/tests/service/async_single_step_exception_test.dart
diff --git a/runtime/observatory/tests/service/async_single_step_exception_test.dart b/runtime/observatory/tests/service/async_single_step_exception_test.dart
index 4307872849759e1cea76113e8e99991a6364df83..07553e549aabdd89362a2f06592dd040f2c56102 100644
--- a/runtime/observatory/tests/service/async_single_step_exception_test.dart
+++ b/runtime/observatory/tests/service/async_single_step_exception_test.dart
@@ -3,21 +3,18 @@
 // BSD-style license that can be found in the LICENSE file.
 // VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
-import 'dart:async';
 import 'dart:developer';
-import 'package:observatory/models.dart' as M;
-import 'package:observatory/service_io.dart';
-import 'package:unittest/unittest.dart';
+
 import 'service_test_common.dart';
 import 'test_helper.dart';
 
-const LINE_A = 23;
-const LINE_B = 24;
-const LINE_C = 30;
-const LINE_D = 32;
-const LINE_E = 35;
-const LINE_F = 38;
-const LINE_G = 40;
+const LINE_A = 20;
+const LINE_B = 21;
+const LINE_C = 27;
+const LINE_D = 29;
+const LINE_E = 32;
+const LINE_F = 35;
+const LINE_G = 37;
 
 helper() async {
   print('helper'); // LINE_A.