Let prefetched resources skip cache revalidation once for a short duration.

net/http/http_network_transaction.cc

Index: net/http/http_network_transaction.cc
diff --git a/net/http/http_network_transaction.cc b/net/http/http_network_transaction.cc
index b4ef356df1531babba69f2198a5e639df910d684..e2a6dda60430b5d0913d04cd90ed8bcaf7f0376d 100644
--- a/net/http/http_network_transaction.cc
+++ b/net/http/http_network_transaction.cc
@@ -173,6 +173,9 @@ int HttpNetworkTransaction::Start(const HttpRequestInfo* request_info,
     proxy_ssl_config_.rev_checking_enabled = false;
   }
 
+  if (request_->load_flags & LOAD_PREFETCH)
+    response_.unused_since_prefetch = true;
+
   // Channel ID is disabled if privacy mode is enabled for this request.
   if (request_->privacy_mode == PRIVACY_MODE_ENABLED)
     server_ssl_config_.channel_id_enabled = false;