Avoid an uncaught error.

lib/src/runner/browser/browser_manager.dart

Index: lib/src/runner/browser/browser_manager.dart
diff --git a/lib/src/runner/browser/browser_manager.dart b/lib/src/runner/browser/browser_manager.dart
index 0442d82bd35819400cdce2c802d588f962c6142b..4504f86b7c9cfc79a071158effc6acd851ad8a46 100644
--- a/lib/src/runner/browser/browser_manager.dart
+++ b/lib/src/runner/browser/browser_manager.dart
@@ -48,12 +48,17 @@ class BrowserManager {
   /// 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].
   ///
@@ -77,6 +82,7 @@ class BrowserManager {
     var suiteChannel;
 
     closeIframe() {
+      if (_closed) return;
       suiteChannel.sink.close();
       _channel.sink.add({
         "command": "closeSuite",