Bug 1756995 - Optimize docshell load end session store collection. r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D146207

docshell/base/nsDocShell.cpp

@@ -5796,8 +5796,8 @@ nsDocShell::OnStateChange(nsIWebProgress* aProgress, nsIRequest* aRequest,
           if (WindowContext* windowContext =
                   mBrowsingContext->GetCurrentWindowContext()) {
             SessionStoreChild::From(windowContext->GetWindowGlobalChild())
-                ->SendResetSessionStore(
-                    mBrowsingContext, mBrowsingContext->GetSessionStoreEpoch());
+                ->ResetSessionStore(mBrowsingContext,
+                                    mBrowsingContext->GetSessionStoreEpoch());
           }
         }
       }
@@ -6538,11 +6538,14 @@ nsresult nsDocShell::EndPageLoad(nsIWebProgress* aProgress,
   if constexpr (SessionStoreUtils::NATIVE_LISTENER) {
     if (WindowContext* windowContext =
             mBrowsingContext->GetCurrentWindowContext()) {
-      // TODO(farre): File bug: From a user perspective this would probably be
-      // just fine to run off the change listener timer. Turns out that a flush
-      // is needed. Several tests depend on this behaviour. Could potentially be
-      // an optimization for later. See Bug 1756995.
-      SessionStoreChangeListener::FlushAllSessionStoreData(windowContext);
+      using Change = SessionStoreChangeListener::Change;
+
+      // We've finished loading the page and now we want to collect all the
+      // session store state that the page is initialized with.
+      SessionStoreChangeListener::CollectSessionStoreData(
+          windowContext,
+          EnumSet<Change>(Change::Input, Change::Scroll, Change::SessionHistory,
+                          Change::WireFrame));
     }
   }