Allows deferral of a URLRequest just before talking to the network, at

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index 68ea7883504fc45070aabdceb059fdbb134ec117..2069d7261eb822370e03a2c4c518f51538f46de6 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -544,6 +544,18 @@ void HttpCache::Transaction::SetWebSocketHandshakeStreamCreateHelper(
     network_trans_->SetWebSocketHandshakeStreamCreateHelper(create_helper);
 }
 
+void HttpCache::Transaction::SetBeforeNetworkStartCallback(
+    const base::Callback<void(bool*)>& callback) {
+  DCHECK(!network_trans_);
+  before_network_start_callback_ = callback;
+}
+
+int HttpCache::Transaction::ResumeNetworkStart() {
+  if (network_trans_)
+    return network_trans_->ResumeNetworkStart();
+  return ERR_UNEXPECTED;
+}
+
 //-----------------------------------------------------------------------------
 
 void HttpCache::Transaction::DoCallback(int rv) {
@@ -865,6 +877,7 @@ int HttpCache::Transaction::DoSendRequest() {
                                                      &network_trans_);
   if (rv != OK)
     return rv;
+  network_trans_->SetBeforeNetworkStartCallback(before_network_start_callback_);
 
   // Old load timing information, if any, is now obsolete.
   old_network_trans_load_timing_.reset();