HTML Imports: Add an UseCounter for <link rel=import async>

Source/core/html/imports/HTMLImportsController.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:
  *
  *     * 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 73 matching lines @@
         if (!ancestor->isRoot() && equalIgnoringFragmentIdentifier(toHTMLImportChild(parent)->url(), url))
             return true;
     }
 
     return false;
 }
 
 HTMLImportChild* HTMLImportsController::createChild(const KURL& url, HTMLImportLoader* loader, HTMLImport* parent, HTMLImportChildClient* client)
 {
     HTMLImport::SyncMode mode = client->isSync() && !makesCycle(parent, url) ? HTMLImport::Sync : HTMLImport::Async;
+    if (mode == HTMLImport::Async)
+        UseCounter::count(root()->document(), UseCounter::HTMLImportsAsyncAttribute);
+
     OwnPtrWillBeRawPtr<HTMLImportChild> child = adoptPtrWillBeNoop(new HTMLImportChild(url, loader, mode));
     child->setClient(client);
     parent->appendImport(child.get());
     loader->addImport(child.get());
     return root()->add(child.release());
 }
 
 HTMLImportChild* HTMLImportsController::load(HTMLImport* parent, HTMLImportChildClient* client, FetchRequest request)
 {
     ASSERT(!request.url().isEmpty() && request.url().isValid());
@@ skipping 68 matching lines @@
 }
 
 void HTMLImportsController::trace(Visitor* visitor)
 {
     visitor->trace(m_root);
     visitor->trace(m_loaders);
     DocumentSupplement::trace(visitor);
 }
 
 } // namespace WebCore