Make AutocompleteErrorEventInit.reason be of type AutocompleteErrorReason (not DOMString)

Source/core/events/AutocompleteErrorEventInit.idl

Index: Source/core/events/AutocompleteErrorEventInit.idl
diff --git a/Source/core/events/AutocompleteErrorEventInit.idl b/Source/core/events/AutocompleteErrorEventInit.idl
index 41cab0e5f73b10d504310a6cfc7262da50d7a62b..840ce04f0c2b8a1e07d42c3a70b8c4406bf4d631 100644
--- a/Source/core/events/AutocompleteErrorEventInit.idl
+++ b/Source/core/events/AutocompleteErrorEventInit.idl
@@ -5,6 +5,5 @@
 // https://html.spec.whatwg.org/multipage/forms.html#the-autocompleteerrorevent-interface
 
 dictionary AutocompleteErrorEventInit : EventInit {
-    // FIXME: According to the spec, "reason" should be AutocompleteErrorReason.
-    DOMString reason;
+    AutocompleteErrorReason reason;
 };