Let unresolved custom element go through CustomElementCallbackQueue.

Source/core/dom/custom/CustomElementResolutionStep.cpp

Index: Source/core/dom/custom/CustomElementResolutionStep.cpp
diff --git a/Source/core/dom/Microtask.cpp b/Source/core/dom/custom/CustomElementResolutionStep.cpp
similarity index 67%
copy from Source/core/dom/Microtask.cpp
copy to Source/core/dom/custom/CustomElementResolutionStep.cpp
index 27cd2178f46cfebf0ba0b3225876edecf7818578..db1b6744d18af8bb577002ded239ad6529652d18 100644
--- a/Source/core/dom/Microtask.cpp
+++ b/Source/core/dom/custom/CustomElementResolutionStep.cpp
@@ -29,28 +29,31 @@
  */
 
 #include "config.h"
-#include "core/dom/Microtask.h"
+#include "core/dom/custom/CustomElementResolutionStep.h"
 
-#include "core/dom/MutationObserver.h"
-#include "core/dom/custom/CustomElementCallbackDispatcher.h"
-#include "wtf/Vector.h"
+#include "core/dom/Element.h"
+#include "core/dom/custom/CustomElementRegistrationContext.h"
 
 namespace WebCore {
 
-void Microtask::performCheckpoint()
+PassOwnPtr<CustomElementResolutionStep> CustomElementResolutionStep::create(PassRefPtr<CustomElementRegistrationContext> context, const CustomElementDescriptor& descriptor)
 {
-    static bool performingCheckpoint = false;
-    if (performingCheckpoint)
-        return;
-    performingCheckpoint = true;
-
-    bool anyWorkDone;
-    do {
-        MutationObserver::deliverAllMutations();
-        anyWorkDone = CustomElementCallbackDispatcher::instance().dispatch();
-    } while (anyWorkDone);
-
-    performingCheckpoint = false;
+    return adoptPtr(new CustomElementResolutionStep(context, descriptor));
+}
+
+CustomElementResolutionStep::CustomElementResolutionStep(PassRefPtr<CustomElementRegistrationContext> context, const CustomElementDescriptor& descriptor)
+    : m_context(context)
+    , m_descriptor(descriptor)
+{
+}
+
+CustomElementResolutionStep::~CustomElementResolutionStep()
+{
+}
+
+void CustomElementResolutionStep::dispatch(Element* element)
+{
+    m_context->resolve(element, m_descriptor);
 }
 
 } // namespace WebCore