Address additional analysis issues in the observatory codebase.

runtime/observatory/tests/service/async_single_step_out_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // 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:developer';
-import 'package:observatory/models.dart' as M;
-import 'package:observatory/service_io.dart';
-import 'package:unittest/unittest.dart';
+import 'dart:io';
+
 import 'service_test_common.dart';
 import 'test_helper.dart';
 
-const LINE_A = 20;
-const LINE_B = 21;
-const LINE_C = 26;
-const LINE_D = 27;
-const LINE_E = 28;
-
 helper() async {
   print('helper'); // LINE_A.
   return null; // LINE_B.
 }
 
 testMain() async {
   debugger();
   print('mmmmm'); // LINE_C.
   await helper(); // LINE_D.
   print('z'); // LINE_E.
 }
 
+final ScriptLineParser lineParser = new ScriptLineParser(Platform.script);
+
 var tests = [
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_C),
+  stoppedAtLine(lineParser.lineFor('LINE_C')),
   stepOver, // print.
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_D),
+  stoppedAtLine(lineParser.lineFor('LINE_D')),
   stepInto,
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_A),
+  stoppedAtLine(lineParser.lineFor('LINE_A')),
   stepOver, // print.
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_B), // return null.
+  stoppedAtLine(lineParser.lineFor('LINE_B')), // return null.
   stepInto, // exit helper via a single step.
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_E), // arrive after the await.
+  stoppedAtLine(lineParser.lineFor('LINE_E')), // arrive after the await.
   resumeIsolate
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);