Make BrowserManager resilient to an early exit.

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 32 matching lines @@
     var suiteChannel = _channel.virtualChannel();
     _channel.sink.add({
       "command": "loadSuite",
       "url": url.toString(),
       "channel": suiteChannel.id
     });
 
     // Create a nested MultiChannel because the iframe will be using a channel
     // wrapped within the host's channel.
     suiteChannel = new MultiChannel(suiteChannel.stream, suiteChannel.sink);
-    return suiteChannel.stream.first.then((response) {
+
+    // The stream may close before emitting a value if the browser is killed
+    // prematurely (e.g. via Control-C).
+    return maybeFirst(suiteChannel.stream).then((response) {
+      if (response == null) return null;
+
       if (response["type"] == "loadException") {
         return new Future.error(new LoadException(path, response["message"]));
       } else if (response["type"] == "error") {
         var asyncError = RemoteException.deserialize(response["error"]);
         return new Future.error(
             new LoadException(path, asyncError.error),
             asyncError.stackTrace);
       }
 
       return new Suite(response["tests"].map((test) {
         var metadata = new Metadata.deserialize(test['metadata']);
         var testChannel = suiteChannel.virtualChannel(test['channel']);
         return new IframeTest(test['name'], metadata, testChannel);
       }), path: path);
     });
   }
 }