Add UseCounter for ServiceWorkerNavigationPreload.

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

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 486 matching lines @@
             mainResourceIdentifier());
         m_frame->document()->addConsoleMessage(consoleMessage);
         cancelLoadAfterCSPDenied(response);
         return;
       }
     }
   }
 
   DCHECK(!m_frame->page()->suspended());
 
+  if (response.didServiceWorkerNavigationPreload()) {
+    UseCounter::count(m_frame->document(),

[tkent, 2017/02/03 00:55:19]

nit: You can use UseCounter::count(m_frame, ...).

[falken, 2017/02/03 01:07:07]

Done.

+                      UseCounter::ServiceWorkerNavigationPreload);
+  }
   m_response = response;
 
   if (isArchiveMIMEType(m_response.mimeType()) &&
       m_mainResource->getDataBufferingPolicy() != BufferData)
     m_mainResource->setDataBufferingPolicy(BufferData);
 
   if (!shouldContinueForResponse()) {
     InspectorInstrumentation::continueWithPolicyIgnore(
         m_frame, this, m_mainResource->identifier(), m_response,
         m_mainResource.get());
@@ skipping 297 matching lines @@
                              m_writer ? m_writer->encoding() : emptyAtom, true,
                              ForceSynchronousParsing);
   if (!source.isNull())
     m_writer->appendReplacingData(source);
   endWriting();
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 }  // namespace blink