Add the ability for DevTools to wrap network transactions.

net/http/http_network_layer.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.
 
 #ifndef NET_HTTP_HTTP_NETWORK_LAYER_H_
 #define NET_HTTP_HTTP_NETWORK_LAYER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 34 matching lines @@
   // HttpTransactionFactory methods:
   virtual int CreateTransaction(RequestPriority priority,
                                 scoped_ptr<HttpTransaction>* trans) OVERRIDE;
   virtual HttpCache* GetCache() OVERRIDE;
   virtual HttpNetworkSession* GetSession() OVERRIDE;
 
   // base::PowerObserver methods:
   virtual void OnSuspend() OVERRIDE;
   virtual void OnResume() OVERRIDE;
 
+  class TransactionFactory {

[szym, 2014/02/27 16:12:37]

This is confusing. HttpNetworkLayer is a HttpTransactionFactory, but a
HttpNetworkLayer::TransactionFactory can override transaction creation.

If you want to control individual transactions, why not swap HttpNetworkLayer in
the HttpCache?

Another idea is to create a dedicated internal HTTP header which instructs the
HttpNetworkTransaction to fail. This is how "Disable cache (while DevTools is
open)" is implemented -- using "Cache-control: no-cache".

+   public:
+    virtual ~TransactionFactory() {}
+
+    // Creates a HttpTransaction object. On success, saves the new
+    // transaction to |*trans| and returns OK.
+    virtual int CreateTransaction(RequestPriority priority,
+                                  HttpNetworkSession* session,
+                                  scoped_ptr<HttpTransaction>* trans) = 0;
+  };
+
+  // Set a global transaction factory. Factory will be used to construct
+  // transactions instead of HttpNetworkTransaction.
+  static void SetTransactionFactory(TransactionFactory*);
+
  private:
   const scoped_refptr<HttpNetworkSession> session_;
   bool suspended_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpNetworkLayer);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_NETWORK_LAYER_H_