Bug 1879001 - Remove the popovertarget attribute or set it to an invalid value should clear the explicitly set attr-element. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D201711

dom/html/nsGenericHTMLElement.cpp

@@ -762,6 +762,8 @@ void nsGenericHTMLElement::AfterSetAttr(int32_t aNamespaceID, nsAtom* aName,
       nsContentUtils::AddScriptRunner(
           NewRunnableMethod("nsGenericHTMLElement::AfterSetPopoverAttr", this,
                             &nsGenericHTMLElement::AfterSetPopoverAttr));
+    } else if (aName == nsGkAtoms::popovertarget) {
+      ClearExplicitlySetAttrElement(nsGkAtoms::popovertarget);
     } else if (aName == nsGkAtoms::dir) {
       auto dir = Directionality::Ltr;
       // A boolean tracking whether we need to recompute our directionality.