pkg/unittest: Add a server for serving test assets to browsers.

lib/src/runner/browser/static/host.dart

Index: lib/src/runner/browser/static/host.dart
diff --git a/lib/src/runner/browser/static/host.dart b/lib/src/runner/browser/static/host.dart
index 357fdfbc5b577887915ce4966a3562af0d0d2279..9858956707d11bfab49bc68d25c3e76e3d4da6f5 100644
--- a/lib/src/runner/browser/static/host.dart
+++ b/lib/src/runner/browser/static/host.dart
@@ -84,10 +84,7 @@ MultiChannel _connectToServer() {
   // The `managerUrl` query parameter contains the WebSocket URL of the remote
   // [BrowserManager] with which this communicates.
   var currentUrl = Uri.parse(window.location.href);
-  var webSocketUrl = currentUrl
-      .resolve(currentUrl.queryParameters['managerUrl'])
-      .replace(scheme: 'ws');
-  var webSocket = new WebSocket(webSocketUrl.toString());
+  var webSocket = new WebSocket(currentUrl.queryParameters['managerUrl']);
 
   var inputController = new StreamController(sync: true);
   webSocket.onMessage.listen(