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

Source/core/dom/custom/CustomElementScheduler.cpp

Index: Source/core/dom/custom/CustomElementScheduler.cpp
diff --git a/Source/core/dom/custom/CustomElementScheduler.cpp b/Source/core/dom/custom/CustomElementScheduler.cpp
index 2583bfa19c979c8ef3276873543ef85049678849..f55803a28179289bfd932722fb0c2ed74818594d 100644
--- a/Source/core/dom/custom/CustomElementScheduler.cpp
+++ b/Source/core/dom/custom/CustomElementScheduler.cpp
@@ -85,7 +85,7 @@ CustomElementMicrotaskImportStep* CustomElementScheduler::scheduleImport(HTMLImp
     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