Let unresolved custom element go through CustomElementCallbackQueue.

Source/core/dom/custom/CustomElementProcessingStep.h

Index: Source/core/dom/custom/CustomElementProcessingStep.h
diff --git a/Source/core/dom/Microtask.h b/Source/core/dom/custom/CustomElementProcessingStep.h
similarity index 78%
copy from Source/core/dom/Microtask.h
copy to Source/core/dom/custom/CustomElementProcessingStep.h
index 27f72cbec01e5795593d3e545a3b5ca3e5c046fa..c92451bae82373f7dc25694b071d9fdbf1af27b5 100644
--- a/Source/core/dom/Microtask.h
+++ b/Source/core/dom/custom/CustomElementProcessingStep.h
@@ -28,19 +28,25 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef Microtask_h
-#define Microtask_h
+#ifndef CustomElementProcessingStep_h
+#define CustomElementProcessingStep_h
+
+#include "wtf/Noncopyable.h"
 
 namespace WebCore {
 
-class Microtask {
+class Element;
+
+class CustomElementProcessingStep {
+    WTF_MAKE_NONCOPYABLE(CustomElementProcessingStep);
 public:
-    static void performCheckpoint();
+    CustomElementProcessingStep() { }
 
-private:
-    explicit Microtask();
+    virtual ~CustomElementProcessingStep() { }
+    virtual void dispatch(Element*) = 0;
+    virtual bool isCreated() const { return false; }

[dominicc (has gone to gerrit), 2013/12/18 08:46:41]

I think we need a better name for this, because prototype swizzle and calling
created are one thing. Also, isCreated might refer to the step itself, but it is
actually about the kind of step. What do you think of isUpgradeStep?

[Hajime Morrita, 2013/12/19 05:06:59]

Sounds good. Adding FIXME for now.

 };
 
 }
 
-#endif // Microtask_h
+#endif // CustomElementProcessingStep_h