Properly initialize an instance variable.

lib/src/runner/browser/browser_manager.dart

 // Copyright (c) 2015, 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 test.runner.browser.browser_manager;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:http_parser/http_parser.dart';
@@ skipping 31 matching lines @@
   /// at once.
   final _pool = new Pool(8);
 
   /// The ID of the next suite to be loaded.
   ///
   /// This is used to ensure that the suites can be referred to consistently
   /// across the client and server.
   int _suiteId = 0;
 
   /// Whether the channel to the browser has closed.
-  bool _closed;
+  bool _closed = false;
 
   /// Creates a new BrowserManager that communicates with [browser] over
   /// [webSocket].
   BrowserManager(this.browser, CompatibleWebSocket webSocket)
       : _channel = new MultiChannel(
           webSocket.map(JSON.decode),
           mapSink(webSocket, JSON.encode)) {
     _channel.stream.listen(null, onDone: () => _closed = true);
   }
 
@@ skipping 79 matching lines @@
 
     return new Suite(response["tests"].map((test) {
       var testMetadata = new Metadata.deserialize(test['metadata']);
       var testChannel = suiteChannel.virtualChannel(test['channel']);
       return new IframeTest(test['name'], testMetadata, testChannel,
           mapper: mapper);
     }), platform: browser, metadata: metadata, path: path,
         onClose: () => closeIframe());
   }
 }