Change rootDirectories to Array to introspect from Dart

lib/src/dartdevc/dartdevc.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.
 
 import 'dart:async';
 import 'dart:convert' show JsonEncoder;
 import 'dart:io';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:barback/barback.dart';
@@ skipping 133 matching lines @@
     var bootstrapContent = new StringBuffer('(function() {\n');
     if (isDebug) {
       bootstrapContent.write('''
 $_currentDirectoryScript
 let modulePaths = ${const JsonEncoder.withIndent(" ").convert(modulePaths)};
 
 if(!window.\$dartLoader) {
    window.\$dartLoader = {
      moduleIdToUrl: new Map(),
      urlToModuleId: new Map(),
-     rootDirectories: new Set(),
+     rootDirectories: new Array(),
    };
 }
 
 let customModulePaths = {};
-window.\$dartLoader.rootDirectories.add(_currentDirectory);
+window.\$dartLoader.rootDirectories.push(_currentDirectory);
 for (let moduleName of Object.getOwnPropertyNames(modulePaths)) {
   let modulePath = modulePaths[moduleName];
   if (modulePath != moduleName) {
     customModulePaths[moduleName] = modulePath;
   }
   var src = _currentDirectory + modulePath + '.js';
   if (window.\$dartLoader.moduleIdToUrl.has(moduleName)) {
     continue;
   }
   \$dartLoader.moduleIdToUrl.set(moduleName, src);
@@ skipping 260 matching lines @@
     } finally {
       for (var id in completers.keys) {
         if (!completers[id].isCompleted) {
           completers[id].completeError(new AssetNotFoundException(id));
         }
       }
     }
   }();
   return futures;
 }