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

Source/core/dom/custom/CustomElementMicrotaskImportStep.h

 /*
  * 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 46 matching lines @@
 
     // API for HTML Imports
     void importDidFinishLoading();
     WeakPtr<CustomElementMicrotaskImportStep> weakPtr() { return m_weakFactory.createWeakPtr(); }
 
 private:
     CustomElementMicrotaskImportStep(HTMLImportChild*);
 
     void didUpgradeAllCustomElements();
     bool shouldWaitForImport() const;
+    bool shouldStopProcessing() const;
 
     // CustomElementMicrotaskStep
     virtual Result process() OVERRIDE FINAL;
 
 #if !defined(NDEBUG)
     virtual void show(unsigned indent) OVERRIDE;
 #endif
-
-    bool m_importFinished;
     WeakPtr<HTMLImportChild> m_import;
     RefPtr<CustomElementMicrotaskQueue> m_queue;
     WeakPtrFactory<CustomElementMicrotaskImportStep> m_weakFactory;
 };
 
 }
 
 #endif // CustomElementMicrotaskImportStep_h