Bug 1716762 - Don't allow focus to move to remote iframe which is display: none; r=emilio

Make it behave the same as in-process iframe.

Differential Revision: https://phabricator.services.mozilla.com/D118002

layout/generic/nsSubDocumentFrame.cpp

@@ -895,6 +895,7 @@ static nsView* BeginSwapDocShellsForViews(nsView* aSibling);
 
 void nsSubDocumentFrame::DestroyFrom(nsIFrame* aDestructRoot,
                                      PostDestroyData& aPostDestroyData) {
+  PropagateIsUnderHiddenEmbedderElementToSubView(true);
   if (mPostedReflowCallback) {
     PresShell()->CancelReflowCallback(this);
     mPostedReflowCallback = false;