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

Source/core/dom/custom/CustomElementScheduler.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 67 matching lines @@
     HTMLImportLoader* loader = element->document().importLoader();
     OwnPtr<CustomElementMicrotaskResolutionStep> step = CustomElementMicrotaskResolutionStep::create(context, element, descriptor);
     CustomElementMicrotaskDispatcher::instance().enqueue(loader, step.release());
 }
 
 CustomElementMicrotaskImportStep* CustomElementScheduler::scheduleImport(HTMLImportChild* import)
 {
     ASSERT(!import->isDone());
     ASSERT(import->parent());
 
-    OwnPtr<CustomElementMicrotaskImportStep> step = CustomElementMicrotaskImportStep::create(import->loader()->microtaskQueue());
+    OwnPtr<CustomElementMicrotaskImportStep> step = CustomElementMicrotaskImportStep::create(import->loader()->ensureMicrotaskQueue());

[dominicc (has gone to gerrit), 2014/04/24 07:28:33]

I thought we were always creating microtask queues for imports now. Don't the
above assertions mean this queue is always in existence at this point?

     CustomElementMicrotaskImportStep* rawStep = step.get();
 
     // Ownership of the new step is transferred to the parent
     // processing step, or the base queue.
     CustomElementMicrotaskDispatcher::instance().enqueue(import->parent()->loader(), step.release());
 
     return rawStep;
 }
 
 CustomElementScheduler& CustomElementScheduler::instance()
@@ skipping 46 matching lines @@
         // The processing stack is active.
         CustomElementCallbackDispatcher::instance().enqueue(&callbackQueue);
         return callbackQueue;
     }
 
     CustomElementMicrotaskDispatcher::instance().enqueue(&callbackQueue);
     return callbackQueue;
 }
 
 } // namespace WebCore