Make Exception a class, not an interface, and remove the const constructor.

runtime/lib/errors_patch.dart

Index: runtime/lib/errors_patch.dart
diff --git a/runtime/lib/errors_patch.dart b/runtime/lib/errors_patch.dart
index d09dc3d9e1cef19fc4cb90190db7aa6363ffdb09..12caeadcb36cca5d2e9557c17dbfd7a87fbed2e9 100644
--- a/runtime/lib/errors_patch.dart
+++ b/runtime/lib/errors_patch.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-patch class NoSuchMethodError {
+patch class Error {
   /* patch */ static String _objectToString(Object object) {
     return Object._toString(object);
   }