Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/bindings/v8/V8RecursionScope.cpp

Index: Source/bindings/v8/V8RecursionScope.cpp
diff --git a/Source/bindings/v8/V8RecursionScope.cpp b/Source/bindings/v8/V8RecursionScope.cpp
index 12cb3b5d854ef62d9aa1098eb7b6610b56325da0..26ebf361eaefee078f122fcd5b99cd60b8d961c1 100644
--- a/Source/bindings/v8/V8RecursionScope.cpp
+++ b/Source/bindings/v8/V8RecursionScope.cpp
@@ -31,8 +31,7 @@
 #include "config.h"
 #include "bindings/v8/V8RecursionScope.h"
 
-#include "core/dom/CustomElementRegistry.h"
-#include "core/dom/MutationObserver.h"
+#include "core/dom/Microtask.h"
 #include "modules/indexeddb/IDBPendingTransactionMonitor.h"
 
 namespace WebCore {
@@ -46,8 +45,7 @@ void V8RecursionScope::didLeaveScriptContext()
     IDBPendingTransactionMonitor::deactivateNewTransactions();
 
     if (m_isDocumentContext) {
-        MutationObserver::deliverAllMutations();
-        CustomElementRegistry::deliverAllLifecycleCallbacks();
+        Microtask::performCheckpoint();
     }
 }