Bug 1888507 - Do not dispatch input, change for detached checkbox, radio. r=dom-core,sefeng

Differential Revision: https://phabricator.services.mozilla.com/D217408

dom/html/HTMLInputElement.cpp

@@ -4106,7 +4106,9 @@ void HTMLInputElement::ActivationBehavior(EventChainPostVisitor& aVisitor) {
     return;
   }
 
-  if (mCheckedIsToggled) {
+  // https://html.spec.whatwg.org/#checkbox-state-(type=checkbox):input-activation-behavior
+  // If element is connected, fire input and change event
+  if (mCheckedIsToggled && IsInComposedDoc()) {
     SetUserInteracted(true);
 
     // Fire input event and then change event.