LibWeb: Create HeapFunction for after_document_populated callback

Now the callback is visited by SafeFunction callback of
deferred_invoke().

Fixes use-after-free ASAN error that happens if you try to reload the
page.

Userland/Libraries/LibWeb/HTML/TraversableNavigable.cpp

@@ -599,10 +599,10 @@ TraversableNavigable::HistoryStepResult TraversableNavigable::apply_the_history_
                 // 7. In parallel, attempt to populate the history entry's document for targetEntry, given navigable, potentiallyTargetSpecificSourceSnapshotParams,
                 //    targetSnapshotParams, with allowPOST set to allowPOST and completionSteps set to queue a global task on the navigation and traversal task source given
                 //    navigable's active window to run afterDocumentPopulated.
-                Platform::EventLoopPlugin::the().deferred_invoke([populated_target_entry, potentially_target_specific_source_snapshot_params, target_snapshot_params, this, allow_POST, navigable, after_document_populated] {
+                Platform::EventLoopPlugin::the().deferred_invoke([populated_target_entry, potentially_target_specific_source_snapshot_params, target_snapshot_params, this, allow_POST, navigable, after_document_populated = JS::create_heap_function(this->heap(), move(after_document_populated))] {
                     navigable->populate_session_history_entry_document(populated_target_entry, *potentially_target_specific_source_snapshot_params, target_snapshot_params, {}, Empty {}, CSPNavigationType::Other, allow_POST, [this, after_document_populated, populated_target_entry]() mutable {
                                  queue_global_task(Task::Source::NavigationAndTraversal, *active_window(), JS::create_heap_function(this->heap(), [after_document_populated, populated_target_entry]() mutable {
-                                     after_document_populated(true, populated_target_entry);
+                                     after_document_populated->function()(true, populated_target_entry);
                                  }));
                              })
                         .release_value_but_fixme_should_propagate_errors();