Count successes of link rel=prefetch

net/url_request/url_request_http_job.cc

Index: net/url_request/url_request_http_job.cc
diff --git a/net/url_request/url_request_http_job.cc b/net/url_request/url_request_http_job.cc
index 51b690824301e8a7bcdb5cbd1f2333d4469858f6..e1b0ffb07bc7c91dd93d80e531f8ff16b900a28a 100644
--- a/net/url_request/url_request_http_job.cc
+++ b/net/url_request/url_request_http_job.cc
@@ -1620,7 +1620,9 @@ void URLRequestHttpJob::RecordPerfHistograms(CompletionCause reason) {
               "Net.HttpJob.TotalTimeCached.Secure.NotQuic", total_time);
         }
       }
-    } else  {
+      if (response_info_->unused_since_prefetch)
+        UMA_HISTOGRAM_COUNTS("Net.Prefetch.HitBytes", prefilter_bytes_read());
+    } else {
       UMA_HISTOGRAM_TIMES("Net.HttpJob.TotalTimeNotCached", total_time);
       if (is_https_google) {
         if (used_quic) {