Bug 1940412 - Add batch removal information to nsIMutationObserver::ContentWillBeRemoved, and use it in some trivial-ish places. r=dom-core,credential-management-reviewers,sefeng

The idea is to use it on the style (via PresShell->RestyleManager) to do
invalidation faster in cases like bug 1940405.

Differential Revision: https://phabricator.services.mozilla.com/D233547

dom/html/HTMLMediaElement.cpp

@@ -2185,7 +2185,8 @@ void HTMLMediaElement::AddSizeOfExcludingThis(nsWindowSizes& aSizes,
   }
 }
 
-void HTMLMediaElement::ContentWillBeRemoved(nsIContent* aChild) {
+void HTMLMediaElement::ContentWillBeRemoved(nsIContent* aChild,
+                                            const BatchRemovalState*) {
   if (aChild == mSourcePointer) {
     mSourcePointer = aChild->GetPreviousSibling();
   }