Bug 444222 - Add a flag 'SetHasLoadedNonInitialDocument' in the BrowsingContext. r=nika

Differential Revision: https://phabricator.services.mozilla.com/D88416

docshell/base/BrowsingContext.h

@@ -150,7 +150,8 @@ class WindowProxyHolder;
    * the value from the top BC! */                                           \
   FIELD(HasSessionHistory, bool)                                             \
   FIELD(UseErrorPages, bool)                                                 \
-  FIELD(PlatformOverride, nsString)
+  FIELD(PlatformOverride, nsString)                                          \
+  FIELD(HasLoadedNonInitialDocument, bool)
 
 // BrowsingContext, in this context, is the cross process replicated
 // environment in which information about documents is stored. In

docshell/base/nsDocShell.cpp

@@ -7772,6 +7772,10 @@ nsresult nsDocShell::CreateContentViewer(const nsACString& aContentType,
 
   NS_ENSURE_SUCCESS(Embed(viewer), NS_ERROR_FAILURE);
 
+  if (!mBrowsingContext->GetHasLoadedNonInitialDocument()) {
+    MOZ_ALWAYS_SUCCEEDS(mBrowsingContext->SetHasLoadedNonInitialDocument(true));
+  }
+
   if (TreatAsBackgroundLoad()) {
     nsCOMPtr<nsIRunnable> triggerParentCheckDocShell =
         NewRunnableMethod("nsDocShell::TriggerParentCheckDocShellIsEmpty", this,