LibWeb: Call process_session_history_traversal_queue on history update

Spec declares that the updates to history should be synchronous on
initial page load and on history pushState/replaceState.

Tests/LibWeb/Text/expected/navigation/history-replace-push-state-race.txt

@@ -0,0 +1 @@
+test done!

Tests/LibWeb/Text/input/navigation/history-replace-push-state-race.html

@@ -0,0 +1,16 @@
+<script src="../include.js"></script>
+<script>
+    asyncTest(done => {
+
+        history.replaceState({}, "hello", "history-replace-push-state-race.html");
+        history.replaceState({}, "hello", "history-replace-push-state-race.html");
+
+        // this test checks a regression for a crash in `finalize_a_same_document_navigation`
+        // when `target_navigable->get_session_history_entries()` does not contain `entry_to_replace` exactly.
+        //
+        // history.replaceState is one possible trigger for the crash.
+
+        println("test done!");
+        done();
+    });
+</script>

Userland/Libraries/LibWeb/HTML/Navigable.cpp

@@ -1877,6 +1877,9 @@ void perform_url_and_history_update_steps(DOM::Document& document, AK::URL new_u
         // 1. Finalize a same-document navigation given traversable, navigable, newEntry, and entryToReplace.
         finalize_a_same_document_navigation(*traversable, *navigable, new_entry, entry_to_replace);
     });
+
+    // FIXME: Implement synchronous session history steps.
+    traversable->process_session_history_traversal_queue();
 }
 
 void Navigable::scroll_offset_did_change()

Userland/Libraries/LibWeb/HTML/NavigableContainer.cpp

@@ -214,9 +214,6 @@ Optional<AK::URL> NavigableContainer::shared_attribute_processing_steps_for_ifra
     // 4. If url matches about:blank and initialInsertion is true, then perform the URL and history update steps given element's content navigable's active document and url.
     if (url_matches_about_blank(url) && initial_insertion) {
         perform_url_and_history_update_steps(*m_content_navigable->active_document(), url);
-        // NOTE: Not in the spec but we need to make sure that "apply the history step" for initial navigation to about:blank
-        //       is applied before subsequent navigation.
-        navigable()->traversable_navigable()->process_session_history_traversal_queue();
     }
 
     // 5. Return url.