Fix dart2js analyze _api_test for dart:io

sdk/lib/io/http_impl.dart

Index: sdk/lib/io/http_impl.dart
diff --git a/sdk/lib/io/http_impl.dart b/sdk/lib/io/http_impl.dart
index 1ed571eadda474cb4de614cdaa1f765847e3b1b9..3e8c34278cc039c840d6d65ae9d954187a3c97fa 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -1597,7 +1597,7 @@ class _Credentials {
   bool used = false;
   Uri uri;
   String realm;
-  HttpClientCredentials credentials;
+  _HttpClientCredentials credentials;
 
   // Digest specific fields.
   String nonce;
@@ -1608,7 +1608,7 @@ class _Credentials {
 
 abstract class _HttpClientCredentials implements HttpClientCredentials {
   _AuthenticationScheme get scheme;
-  void authorize(HttpClientRequest request);
+  void authorize(_Credentials credentials, HttpClientRequest request);
 }