Bug 1597486 - Fix uses of nsIDocShellTreeItem in nsMenuPopupFrame::Init(). r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D61426

--HG--
extra : moz-landing-system : lando

layout/xul/nsMenuPopupFrame.cpp

@@ -164,8 +164,7 @@ void nsMenuPopupFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
     mPopupType = ePopupTypeTooltip;
   }
 
-  nsCOMPtr<nsIDocShellTreeItem> dsti = PresContext()->GetDocShell();
-  if (dsti && dsti->ItemType() == nsIDocShellTreeItem::typeChrome) {
+  if (PresContext()->IsChrome()) {
     mInContentShell = false;
   }