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..c08fba7c855efb188047777c0fb263a92d5f16c7 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 {
@@ -45,10 +44,8 @@ void V8RecursionScope::didLeaveScriptContext()
     // set to true, but the flag becomes false when control returns to the event loop.
     IDBPendingTransactionMonitor::deactivateNewTransactions();
 
-    if (m_isDocumentContext) {
-        MutationObserver::deliverAllMutations();
-        CustomElementRegistry::deliverAllLifecycleCallbacks();
-    }
+    if (m_isDocumentContext)
+        Microtask::performCheckpoint();
 }
 
 } // namespace WebCore