Verify the default locale in case we're given an invalid one and need to fall back.

pkg/intl/test/message_extraction/foo_messages_all.dart

Index: pkg/intl/test/message_extraction/foo_messages_all.dart
diff --git a/pkg/intl/test/message_extraction/foo_messages_all.dart b/pkg/intl/test/message_extraction/foo_messages_all.dart
index 1568a649950c02eb744bfb65c56164eb5f8292e8..98e47e87afb7c18735029b2f521292a3ccb00a76 100644
--- a/pkg/intl/test/message_extraction/foo_messages_all.dart
+++ b/pkg/intl/test/message_extraction/foo_messages_all.dart
@@ -34,7 +34,8 @@ Future initializeMessages(String localeName) {
 }
 
 MessageLookupByLibrary _findGeneratedMessagesFor(locale) {
-  var actualLocale = Intl.verifiedLocale(locale, (x) => _findExact(x) != null);
+  var actualLocale = Intl.verifiedLocale(locale, (x) => _findExact(x) != null,
+      onFailure: (_) => null);
   if (actualLocale == null) return null;
   return _findExact(actualLocale);
 }