Bug 1596958 - Synchronize layouthistorystate to parent process, r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D53288

layout/base/nsDocumentViewer.cpp

@@ -1697,6 +1697,7 @@ nsDocumentViewer::Close(nsISHEntry* aSHEntry) {
 
 static void DetachContainerRecurse(nsIDocShell* aShell) {
   // Unhook this docshell's presentation
+  aShell->SynchronizeLayoutHistoryState();
   nsCOMPtr<nsIContentViewer> viewer;
   aShell->GetContentViewer(getter_AddRefs(viewer));
   if (viewer) {
@@ -1824,6 +1825,7 @@ nsDocumentViewer::Destroy() {
     // and shEntry has no window state at this point we'll be ok; we just won't
     // cache ourselves.
     shEntry->SyncPresentationState();
+    shEntry->SynchronizeLayoutHistoryState();
 
     // Shut down accessibility for the document before we start to tear it down.
 #ifdef ACCESSIBILITY