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

Source/core/html/imports/HTMLImport.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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 91 matching lines @@
         Sync  = 0,
         Async = 1
     };
 
     virtual ~HTMLImport() { }
 
     HTMLImport* root();
     bool precedes(HTMLImport*);
     bool isRoot() const { return !isChild(); }
     bool isSync() const { return SyncMode(m_sync) == Sync; }
+    bool formsCycle() const;

[dominicc (has gone to gerrit), 2014/04/30 23:57:20]

Why is this new concept needed now?

     const HTMLImportState& state() const { return m_state; }
 
     void appendImport(HTMLImport*);
 
     virtual bool isChild() const { return false; }
     virtual Document* document() const = 0;
     virtual bool isDone() const = 0; // FIXME: Should be renamed to haveFinishedLoading()
     virtual HTMLImportLoader* loader() const { return 0; }
     virtual void stateWillChange() { }
     virtual void stateDidChange();
@@ skipping 14 matching lines @@
 #endif
 
 private:
     HTMLImportState m_state;
     unsigned m_sync : 1;
 };
 
 } // namespace WebCore
 
 #endif // HTMLImport_h