Remove AsyncError with Expando.

pkg/http/test/safe_http_server.dart

Index: pkg/http/test/safe_http_server.dart
diff --git a/pkg/http/test/safe_http_server.dart b/pkg/http/test/safe_http_server.dart
index 8acc1abb6117bd483a789ffe542c493a8d7a3a4e..356d835f46065e1c953ebd4576e3891e8dd55522 100644
--- a/pkg/http/test/safe_http_server.dart
+++ b/pkg/http/test/safe_http_server.dart
@@ -42,13 +42,12 @@ class SafeHttpServer extends StreamView<HttpRequest> implements HttpServer {
   HttpConnectionsInfo connectionsInfo() => _inner.connectionsInfo();
 
   StreamSubscription<HttpRequest> listen(void onData(HttpRequest value),
-      {void onError(AsyncError error), void onDone(),
+      {void onError(error), void onDone(),
       bool unsubscribeOnError: false}) {
     var subscription;
     subscription = super.listen((request) {
       onData(new _HttpRequestWrapper(request));
-    }, onError: (e) {
-      var error = e.error;
+    }, onError: (error) {
       // Ignore socket error 104, which is caused by a request being cancelled
       // before it writes any headers. There's no reason to care about such
       // requests.
@@ -58,7 +57,7 @@ class SafeHttpServer extends StreamView<HttpRequest> implements HttpServer {
       // Manually handle unsubscribeOnError so the above (ignored) errors don't
       // cause unsubscription.
       if (unsubscribeOnError) subscription.cancel();
-      if (onError != null) onError(e);
+      if (onError != null) onError(error);
     }, onDone: onDone);
     return subscription;
   }