anchor.diff:      DateTime end = new DateTime.now();
       int elapsed = end.difference(_testStarts[testCase.id]).inMilliseconds;
       if (testCase.stackTrace != null) {
  -      var message = json.stringify(testCase.stackTrace.frames.map((frame) {
  +      var message = JSON.encode(testCase.stackTrace.frames.map((frame) {
           return <String, dynamic>{
             "uri": frame.uri.toString(),
             "line": frame.line,
  
positive.code:     if (msg.messageType == _Message.LOG) {
        logMessage(e.data);
      } else if (msg.messageType == _Message.STACK) {
        _stack = new Trace(json.parse(msg.body).map((frame) {
          return new Frame(
              Uri.parse(frame['uri']),
              frame['line'],
  
negative.code: 
  import 'dart:html';
  import 'dart:async';
  import 'dart:convert';
  
  import 'package:stack_trace/stack_trace.dart';
  
  