Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/WebKit/chromium/src/WebKit.cpp

Index: Source/WebKit/chromium/src/WebKit.cpp
diff --git a/Source/WebKit/chromium/src/WebKit.cpp b/Source/WebKit/chromium/src/WebKit.cpp
index ae2a9854a0f73dbef78184a52fd5441a5b0627d0..c2a1c326ec59edcc5e91dd70e20ddbfaef969ce0 100644
--- a/Source/WebKit/chromium/src/WebKit.cpp
+++ b/Source/WebKit/chromium/src/WebKit.cpp
@@ -38,8 +38,7 @@
 #include "bindings/v8/V8Binding.h"
 #include "bindings/v8/V8RecursionScope.h"
 #include "core/Init.h"
-#include "core/dom/CustomElementRegistry.h"
-#include "core/dom/MutationObserver.h"
+#include "core/dom/Microtask.h"
 #include "core/page/Frame.h"
 #include "core/page/Page.h"
 #include "core/page/Settings.h"
@@ -70,8 +69,7 @@ public:
     virtual void willProcessTask() { }
     virtual void didProcessTask()
     {
-        WebCore::CustomElementRegistry::deliverAllLifecycleCallbacks();
-        WebCore::MutationObserver::deliverAllMutations();
+        WebCore::Microtask::performCheckpoint();
     }
 };