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

net/http/http_cache_transaction.h

 // Copyright (c) 2012 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.
 
 // This file declares HttpCache::Transaction, a private class of HttpCache so
 // it should only be included by http_cache.cc
 
 #ifndef NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 #define NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 
@@ skipping 113 matching lines @@
   virtual int64 GetTotalReceivedBytes() const OVERRIDE;
   virtual void DoneReading() OVERRIDE;
   virtual const HttpResponseInfo* GetResponseInfo() const OVERRIDE;
   virtual LoadState GetLoadState() const OVERRIDE;
   virtual UploadProgress GetUploadProgress(void) const OVERRIDE;
   virtual bool GetLoadTimingInfo(
       LoadTimingInfo* load_timing_info) const OVERRIDE;
   virtual void SetPriority(RequestPriority priority) OVERRIDE;
   virtual void SetWebSocketHandshakeStreamCreateHelper(
       net::WebSocketHandshakeStreamBase::CreateHelper* create_helper) OVERRIDE;
+  virtual void SetBeforeNetworkStartCallback(
+      const BeforeNetworkStartCallback& callback) OVERRIDE;
+  virtual int ResumeNetworkStart() OVERRIDE;
 
  private:
   static const size_t kNumValidationHeaders = 2;
   // Helper struct to pair a header name with its value, for
   // headers used to validate cache entries.
   struct ValidationHeaders {
     ValidationHeaders() : initialized(false) {}
 
     std::string values[kNumValidationHeaders];
     bool initialized;
@@ skipping 287 matching lines @@
   // before the caller requests load timing information.
   scoped_ptr<LoadTimingInfo> old_network_trans_load_timing_;
 
   // The helper object to use to create WebSocketHandshakeStreamBase
   // objects. Only relevant when establishing a WebSocket connection.
   // This is passed to the underlying network transaction. It is stored here in
   // case the transaction does not exist yet.
   WebSocketHandshakeStreamBase::CreateHelper*
       websocket_handshake_stream_base_create_helper_;
 
+  BeforeNetworkStartCallback before_network_start_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_