Reapply expanding overloaded functions into separate functions.

tests/html/form_data_test.dart

Index: tests/html/form_data_test.dart
diff --git a/tests/html/form_data_test.dart b/tests/html/form_data_test.dart
index 301781082cd61bc6b70d55509fa60ccb8d80810b..0cbe6bc4968693e2b79587649fb420bb2d3e90ee 100644
--- a/tests/html/form_data_test.dart
+++ b/tests/html/form_data_test.dart
@@ -53,7 +53,7 @@ void main() {
         form.append('test', '1');
         form.append('username', 'Elmo');
         form.append('address', '1 Sesame Street');
-        form.append('password', '123456', 'foo');
+        form.append('password', '123456');
         expect(form, isNotNull);
       });