Bug 1665710: don't update session history for about:blank transient pages r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D90589

docshell/base/nsDocShell.cpp

@@ -280,7 +280,7 @@ static mozilla::LazyLogModule gDocShellAndDOMWindowLeakLogging(
 #endif
 static mozilla::LazyLogModule gDocShellLeakLog("nsDocShellLeak");
 extern mozilla::LazyLogModule gPageCacheLog;
-static mozilla::LazyLogModule gSHLog("SessionHistory");
+mozilla::LazyLogModule gSHLog("SessionHistory");
 
 const char kBrandBundleURL[] = "chrome://branding/locale/brand.properties";
 const char kAppstringsBundleURL[] =
@@ -5689,7 +5689,8 @@ nsresult nsDocShell::RefreshURIFromQueue() {
 }
 
 nsresult nsDocShell::Embed(nsIContentViewer* aContentViewer,
-                           WindowGlobalChild* aWindowActor) {
+                           WindowGlobalChild* aWindowActor,
+                           bool aIsTransientAboutBlank) {
   // Save the LayoutHistoryState of the previous document, before
   // setting up new document
   PersistLayoutHistoryState();
@@ -5714,7 +5715,8 @@ nsresult nsDocShell::Embed(nsIContentViewer* aContentViewer,
     SetHistoryEntryAndUpdateBC(Nothing(), Some<nsISHEntry*>(mLSHE));
   }
 
-  if (StaticPrefs::fission_sessionHistoryInParent()) {
+  if (!aIsTransientAboutBlank &&
+      StaticPrefs::fission_sessionHistoryInParent()) {
     MOZ_LOG(gSHLog, LogLevel::Debug, ("document %p Embed", this));
     MoveLoadingToActiveEntry(mLoadType != LOAD_ERROR_PAGE);
   }
@@ -6764,7 +6766,7 @@ nsresult nsDocShell::CreateAboutBlankContentViewer(
       // hook 'em up
       if (viewer) {
         viewer->SetContainer(this);
-        rv = Embed(viewer, aActor);
+        rv = Embed(viewer, aActor, true);
         NS_ENSURE_SUCCESS(rv, rv);
 
         SetCurrentURI(blankDoc->GetDocumentURI(), nullptr, true, 0);