Bug 1539017 - Update the parent for the outside ::marker frame in case we moved it to a ColumnSetWrapperFrame ancestor. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D25313

layout/base/nsCSSFrameConstructor.cpp

@@ -9815,6 +9815,7 @@ void nsCSSFrameConstructor::ProcessChildren(
               listItem = do_QueryFrame(grandParent);
               MOZ_ASSERT(listItem, "ColumnSetWrapperFrame is expected to be "
                                    "a nsBlockFrame subclass");
+              childFrame->SetParent(listItem);
             }
           }
           listItem->SetMarkerFrameForListItem(childFrame);