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

Source/core/dom/custom/CustomElementMicrotaskStep.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 24 matching lines @@
 
 namespace WebCore {
 
 class CustomElementMicrotaskStep {
     WTF_MAKE_NONCOPYABLE(CustomElementMicrotaskStep);
 public:
     CustomElementMicrotaskStep() { }
     virtual ~CustomElementMicrotaskStep() { }
 
     enum Result {
-        Continue   = 1 << 0,
-        ShouldStop = 1 << 1
+        ContinueWithRemoving = 0,
+        ShouldStop           = 1 << 0,
+        ShouldRemain         = 1 << 1
     };
 
     virtual Result process() = 0;
 
 #if !defined(NDEBUG)
     virtual void show(unsigned indent) = 0;
 #endif
 };
 
 }
 
 #endif // CustomElementMicrotaskStep_h