Let unresolved custom element go through CustomElementCallbackQueue.

Source/core/dom/custom/CustomElementCallbackScheduler.cpp

Index: Source/core/dom/custom/CustomElementCallbackScheduler.cpp
diff --git a/Source/core/dom/custom/CustomElementCallbackScheduler.cpp b/Source/core/dom/custom/CustomElementCallbackScheduler.cpp
index 2d36478ea86e92a6136e7c272fe8f44fb9d635e8..ae7edf880c9ff886ac3155c6ddf50dcb07186833 100644
--- a/Source/core/dom/custom/CustomElementCallbackScheduler.cpp
+++ b/Source/core/dom/custom/CustomElementCallbackScheduler.cpp
@@ -33,7 +33,10 @@
 
 #include "core/dom/Element.h"
 #include "core/dom/custom/CustomElementCallbackDispatcher.h"
+#include "core/dom/custom/CustomElementCallbackInvocation.h"
 #include "core/dom/custom/CustomElementLifecycleCallbacks.h"
+#include "core/dom/custom/CustomElementRegistrationContext.h"
+#include "core/dom/custom/CustomElementResolutionStep.h"
 
 namespace WebCore {
 
@@ -73,6 +76,13 @@ void CustomElementCallbackScheduler::scheduleLeftViewCallback(PassRefPtr<CustomE
     queue->append(CustomElementCallbackInvocation::createInvocation(callbacks, CustomElementLifecycleCallbacks::LeftView));
 }
 
+void CustomElementCallbackScheduler::scheduleResolutionStep(const CustomElementDescriptor& descriptor, PassRefPtr<Element> element)
+{
+    RefPtr<CustomElementRegistrationContext> context = element->document().registrationContext();
+    CustomElementCallbackQueue* queue = instance().schedule(element);
+    queue->append(CustomElementResolutionStep::create(context.release(), descriptor));
+}
+
 CustomElementCallbackScheduler& CustomElementCallbackScheduler::instance()
 {
     DEFINE_STATIC_LOCAL(CustomElementCallbackScheduler, instance, ());