Add a use counter for Link rel=serviceworker headers.

third_party/WebKit/Source/core/loader/LinkLoader.cpp

 /*
  * Copyright (C) 2011 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 394 matching lines @@
           (viewportDescriptionWrapper && viewportDescriptionWrapper->set)
               ? &(viewportDescriptionWrapper->description)
               : nullptr;
 
       preloadIfNeeded(relAttribute, url, *document, header.as(),
                       header.mimeType(), header.media(),
                       crossOriginAttributeValue(header.crossOrigin()),
                       LinkCalledFromHeader, errorOccurred, viewportDescription,
                       ReferrerPolicyDefault);
     }
+    if (relAttribute.isServiceWorker()) {
+      UseCounter::count(*document, UseCounter::LinkHeaderServiceWorker);
+    }
     // TODO(yoav): Add more supported headers as needed.
   }
 }
 
 bool LinkLoader::loadLink(const LinkRelAttribute& relAttribute,
                           CrossOriginAttributeValue crossOrigin,
                           const String& type,
                           const String& as,
                           const String& media,
                           ReferrerPolicy referrerPolicy,
@@ skipping 52 matching lines @@
 
 DEFINE_TRACE(LinkLoader) {
   visitor->trace(m_client);
   visitor->trace(m_prerender);
   visitor->trace(m_linkPreloadResourceClient);
   ResourceOwner<Resource, ResourceClient>::trace(visitor);
   PrerenderClient::trace(visitor);
 }
 
 }  // namespace blink