Part 7: Bug 1700623 - Make session storage session store work with Fission. r=nika

Use the newly added session storage data getter to access the session
storage in the parent and store it in session store without a round
trip to content processes.

Depends on D111433

Differential Revision: https://phabricator.services.mozilla.com/D111434

docshell/base/BrowsingContext.cpp

@@ -3025,6 +3025,14 @@ void BrowsingContext::DidSet(FieldIndex<IDX_CurrentInnerWindowId>) {
         prevWindowContext->Canonical()->DidBecomeCurrentWindowGlobal(false);
       }
       if (mCurrentWindowContext) {
+        // We set a timer when we set the current inner window. This
+        // will then flush the session storage to session store to
+        // make sure that we don't miss to store session storage to
+        // session store that is a result of navigation. This is due
+        // to Bug 1700623. We wish to fix this in Bug 1711886, where
+        // making sure to store everything would make this timer
+        // unnecessary.
+        Canonical()->MaybeScheduleSessionStoreUpdate();
         mCurrentWindowContext->Canonical()->DidBecomeCurrentWindowGlobal(true);
       }
     }