Allow Suites to be added to an Engine over time.

lib/src/runner/browser/browser.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;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 39 matching lines @@
   Browser(Future<Process> startBrowser()) {
     // Don't return a Future here because there's no need for the caller to wait
     // for the process to actually start. They should just wait for the HTTP
     // request instead.
     runZoned(() async {
       var process = await startBrowser();
       _processCompleter.complete(process);
 
       var exitCode = await process.exitCode;
 
+      // This hack dodges an otherwise intractable race condition. When the user
+      // presses Control-C, the signal is sent to the browser and the test
+      // runner at the same time. It's possible for the browser to exit before
+      // the [Browser.close] is called, which would trigger the error below.
+      //
+      // A negative exit code signals that the process exited due to a signal.
+      // However, it's possible that this signal didn't come from the user's
+      // Control-C, in which case we do want to throw the error. The only way to
+      // resolve the ambiguity is to wait a brief amount of time and see if this
+      // browser is actually closed.
+      if (!_closed && exitCode < 0) {
+        await new Future.delayed(new Duration(milliseconds: 200));
+      }
+
       if (!_closed && exitCode != 0) {
         throw new ApplicationException(
             "$name failed with exit code $exitCode.");
       }
 
       _onExitCompleter.complete();
     }, onError: (error, stackTrace) {
       // Ignore any errors after the browser has been closed.
       if (_closed) return;
 
@@ skipping 13 matching lines @@
   /// Returns the same [Future] as [onExit], except that it won't emit
   /// exceptions.
   Future close() {
     _closed = true;
     _process.then((process) => process.kill());
 
     // Swallow exceptions. The user should explicitly use [onExit] for these.
     return onExit.catchError((_) {});
   }
 }