Refactor service tests in preparation of running on sky_shell

runtime/observatory/tests/service/async_next_test.dart

Index: runtime/observatory/tests/service/async_next_test.dart
diff --git a/runtime/observatory/tests/service/async_next_test.dart b/runtime/observatory/tests/service/async_next_test.dart
index 3ac354d4549b8d592ee11c151bffe1d2096d2fe1..4fefcca786308aafde726c30d981abdb9c819b6b 100644
--- a/runtime/observatory/tests/service/async_next_test.dart
+++ b/runtime/observatory/tests/service/async_next_test.dart
@@ -4,16 +4,21 @@
 // VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
 
 import 'package:observatory/service_io.dart';
+import 'service_test_common.dart';
 import 'test_helper.dart';
 import 'dart:developer';
 
+const int LINE_A = 19;
+const int LINE_B = 20;
+const int LINE_C = 21;
+
 foo() async { }
 
 doAsync(stop) async {
   if (stop) debugger();
-  await foo(); // Line 14.
-  await foo(); // Line 15.
-  await foo(); // Line 16.
+  await foo(); // Line A.
+  await foo(); // Line B.
+  await foo(); // Line C.
   return null;
 }
 
@@ -31,15 +36,15 @@ asyncNext(Isolate isolate) async {
 
 var tests = [
   hasStoppedAtBreakpoint,
-  stoppedAtLine(14),
+  stoppedAtLine(LINE_A),
   stepOver, // foo()
   asyncNext,
   hasStoppedAtBreakpoint,
-  stoppedAtLine(15),
+  stoppedAtLine(LINE_B),
   stepOver, // foo()
   asyncNext,
   hasStoppedAtBreakpoint,
-  stoppedAtLine(16),
+  stoppedAtLine(LINE_C),
   resumeIsolate,
 ];