Add Windows support.

test/runner/browser/content_shell_test.dart

Index: test/runner/browser/content_shell_test.dart
diff --git a/test/runner/browser/content_shell_test.dart b/test/runner/browser/content_shell_test.dart
index 064eea6bdd80445bed4a525ab06afbbb78ef4efd..5139bce70b4e9d4d6c213bf308da30d2c00dc1f6 100644
--- a/test/runner/browser/content_shell_test.dart
+++ b/test/runner/browser/content_shell_test.dart
@@ -14,6 +14,7 @@ import 'package:test/src/util/io.dart';
 import 'package:test/src/utils.dart';
 import 'package:test/test.dart';
 
+import '../../io.dart';
 import '../../utils.dart';
 
 void main() {
@@ -143,6 +144,6 @@ webSocket.onOpen.first.then((_) =>
     var contentShell = new ContentShell("http://dart-lang.org",
         executable: "_does_not_exist");
     expect(contentShell.onExit, throwsA(isApplicationException(startsWith(
-        "Failed to start content shell: No such file or directory"))));
+        "Failed to start content shell: $noSuchFileMessage"))));
   });
 }