Keep track of how many documents had a resource intercepted by foreign fetch.

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

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013, Intel Corporation
  *
  * 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.
@@ skipping 637 matching lines @@
 {
     ASSERT(m_client);
 
     if (!m_actualRequest.isNull()) {
         reportResponseReceived(identifier, response);
         handlePreflightResponse(response);
         return;
     }
 
     if (response.wasFetchedViaServiceWorker()) {
+        if (response.wasFetchedViaForeignFetch())
+            UseCounter::count(m_document, UseCounter::ForeignFetchInterception);
         if (response.wasFallbackRequiredByServiceWorker()) {
             // At this point we must have m_fallbackRequestForServiceWorker.
             // (For SharedWorker the request won't be CORS or CORS-with-preflight,
             // therefore fallback-to-network is handled in the browser process
             // when the ServiceWorker does not call respondWith().)
             ASSERT(!m_fallbackRequestForServiceWorker.isNull());
             reportResponseReceived(identifier, response);
             loadFallbackRequestForServiceWorker();
             return;
         }
@@ skipping 303 matching lines @@
 
 DEFINE_TRACE(DocumentThreadableLoader)
 {
     visitor->trace(m_resource);
     visitor->trace(m_document);
     ThreadableLoader::trace(visitor);
     RawResourceClient::trace(visitor);
 }
 
 } // namespace blink