Cpp bindings: Return false from Validator::Accept() on unrecognized message or invalid flags

mojo/public/cpp/bindings/lib/validation_errors.cc

Index: mojo/public/cpp/bindings/lib/validation_errors.cc
diff --git a/mojo/public/cpp/bindings/lib/validation_errors.cc b/mojo/public/cpp/bindings/lib/validation_errors.cc
index d1d723a15529dfe464965454de6a1b53ede304fe..6b288effff8d958c6f6b73427e29ee23f5c5b4a1 100644
--- a/mojo/public/cpp/bindings/lib/validation_errors.cc
+++ b/mojo/public/cpp/bindings/lib/validation_errors.cc
@@ -44,6 +44,8 @@ const char* ValidationErrorToString(ValidationError error) {
       return "VALIDATION_ERROR_DIFFERENT_SIZED_ARRAYS_IN_MAP";
     case VALIDATION_ERROR_UNKOWN_UNION_TAG:
       return "VALIDATION_ERROR_UNKOWN_UNION_TAG";
+    case VALIDATION_ERROR_UNKOWN_METHOD:
+      return "VALIDATION_ERROR_UNKOWN_METHOD";
   }
 
   return "Unknown error";