REGRESSION(r171966): Custom elements in async imports don't get upgrade.

Source/core/dom/custom/CustomElementMicrotaskResolutionStep.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 40 matching lines @@
 CustomElementMicrotaskResolutionStep::~CustomElementMicrotaskResolutionStep()
 {
 }
 
 CustomElementMicrotaskStep::Result CustomElementMicrotaskResolutionStep::process()
 {
     m_context->resolve(m_element.get(), m_descriptor);
     return CustomElementMicrotaskStep::Continue;
 }
 
+#if !defined(NDEBUG)
+
+void CustomElementMicrotaskResolutionStep::show(unsigned indent)
+{
+    for (unsigned i = 0; i < indent; ++i)
+        fprintf(stderr, " ");
+    fprintf(stderr, "Resolution: ");
+    m_element->outerHTML().show();
+}
+
+#endif
+
 } // namespace WebCore