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

net/http/http_transaction.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_HTTP_HTTP_TRANSACTION_H_
 #define NET_HTTP_HTTP_TRANSACTION_H_
 
 #include "net/base/completion_callback.h"
 #include "net/base/load_states.h"
 #include "net/base/net_export.h"
@@ skipping 126 matching lines @@
   virtual bool GetLoadTimingInfo(LoadTimingInfo* load_timing_info) const = 0;
 
   // Called when the priority of the parent job changes.
   virtual void SetPriority(RequestPriority priority) = 0;
 
   // Set the WebSocketHandshakeStreamBase::CreateHelper to be used for the
   // request.  Only relevant to WebSocket transactions. Must be called before
   // Start(). Ownership of |create_helper| remains with the caller.
   virtual void SetWebSocketHandshakeStreamCreateHelper(
       WebSocketHandshakeStreamBase::CreateHelper* create_helper) = 0;
+
+  // Set the callback to receive notification just before network use.
+  virtual void SetBeforeNetworkStartCallback(
+      const base::Callback<void(bool*)>& callback) = 0;
+
+  // Resumes the transaction after being deferred.
+  virtual int ResumeNetworkStart() = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_TRANSACTION_H_