Filter frames from debugger stack based on visibility rather than "debuggability" (steppability).

tests/standalone/vmservice/isolate_stacktrace_command_test.dart

 // Copyright (c) 2013, 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.
 
 library isolate_stacktrace_command_test;
 
 import 'test_helper.dart';
 import 'package:expect/expect.dart';
 
 class StacktraceTest extends VmServiceRequestHelper {
   StacktraceTest(port, id) :
       super('http://127.0.0.1:$port/isolates/$id/stacktrace');
 
   onRequestCompleted(Map reply) {
     Expect.equals('StackTrace', reply['type'], 'Not a StackTrace message.');
-    Expect.equals(4, reply['members'].length, 'Stacktrace is wrong length.');
+    Expect.isTrue(4 <= reply['members'].length, 'Stacktrace is wrong length.');
+    // The number of frames involved in isolate message dispatch is an
+    // implementation detail. Only check that we got all the frames for user
+    // code.
     Expect.equals('a', reply['members'][0]['name']);
     Expect.equals('b', reply['members'][1]['name']);
     Expect.equals('c', reply['members'][2]['name']);
     Expect.equals('myIsolateName', reply['members'][3]['name']);
   }
 }
 
 class IsolateListTest extends VmServiceRequestHelper {
   IsolateListTest(port) : super('http://127.0.0.1:$port/isolates');
 
@@ skipping 11 matching lines @@
   process.launch().then((port) {
     var test = new IsolateListTest(port);
     test.makeRequest().then((_) {
       var stacktraceTest = new StacktraceTest(port, test._isolateId);
       stacktraceTest.makeRequest().then((_) {
         process.requestExit();
       });
     });
   });
 }