Mark dart: libraries as not debuggable (by default)

runtime/observatory/tests/service/positive_token_pos_test.dart

 // Copyright (c) 2016, 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
 
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'service_test_common.dart';
 import 'test_helper.dart';
 
 helper() async {  // Line 12, Col 16 is the open brace.
 }
 
 testMain() {
   debugger();
   helper();  // Line 17, Col 3 is the position of the function call.
 }
 
 var tests = [
   hasStoppedAtBreakpoint,
+  markDartColonLibrariesDebuggable,
   stoppedAtLine(17),
   stepInto,
 
   (Isolate isolate) async {
     ServiceMap stack = await isolate.getStack();
     expect(stack['frames'].length, greaterThan(3));
 
     var frame = stack['frames'][0];
     expect(frame.function.name, equals('Completer.sync'));
     expect(await frame.location.getLine(), greaterThan(0));
     expect(await frame.location.getColumn(), greaterThan(0));
 
     // We used to return a negative token position for this frame.
     // See issue #27128.
     frame = stack['frames'][1];
     expect(frame.function.name, equals('helper'));
     expect(await frame.location.getLine(), equals(12));
     expect(await frame.location.getColumn(), equals(16));
 
     frame = stack['frames'][2];
     expect(frame.function.name, equals('testMain'));
     expect(await frame.location.getLine(), equals(17));
     expect(await frame.location.getColumn(), equals(3));
   }
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);