Avoid an uncaught error.

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 30 matching lines @@
   /// once, and we want a timeout in case they fail so we only wait for so many
   /// 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;
+
   /// 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));
+          mapSink(webSocket, JSON.encode)) {
+    _channel.stream.listen(null, onDone: () => _closed = true);

[kevmoo, 2015/07/14 23:33:38]

feels weird, but I guess Stream doesn't have a done property.

+  }
 
   /// Tells the browser the load a test suite from the URL [url].
   ///
   /// [url] should be an HTML page with a reference to the JS-compiled test
   /// suite. [path] is the path of the original test suite file, which is used
   /// for reporting. [metadata] is the parsed metadata for the test suite.
   ///
   /// If [mapper] is passed, it's used to map stack traces for errors coming
   /// from this test suite.
   Future<Suite> loadSuite(String path, Uri url, Metadata metadata,
       {StackTraceMapper mapper}) async {
     url = url.replace(fragment: Uri.encodeFull(JSON.encode({
       "metadata": metadata.serialize(),
       "browser": browser.identifier
     })));
 
     // The stream may close before emitting a value if the browser is killed
     // prematurely (e.g. via Control-C).
     var suiteVirtualChannel = _channel.virtualChannel();
     var suiteId = _suiteId++;
     var suiteChannel;
 
     closeIframe() {
+      if (_closed) return;
       suiteChannel.sink.close();
       _channel.sink.add({
         "command": "closeSuite",
         "id": suiteId
       });
     }
 
     var response = await _pool.withResource(() {
       _channel.sink.add({
         "command": "loadSuite",
@@ skipping 45 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);
     }), metadata: metadata, path: path, onClose: () => closeIframe());
   }
 }