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

net/http/http_cache_transaction.h

Index: net/http/http_cache_transaction.h
diff --git a/net/http/http_cache_transaction.h b/net/http/http_cache_transaction.h
index 9c69817f98c5c5dde45e1d62b5fb85316936c220..4e44130ed022f03df9f559f33136aac547ac7e1c 100644
--- a/net/http/http_cache_transaction.h
+++ b/net/http/http_cache_transaction.h
@@ -131,6 +131,9 @@ class HttpCache::Transaction : public HttpTransaction {
   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;
@@ -438,6 +441,8 @@ class HttpCache::Transaction : public HttpTransaction {
   WebSocketHandshakeStreamBase::CreateHelper*
       websocket_handshake_stream_base_create_helper_;
 
+  BeforeNetworkStartCallback before_network_start_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };