Add the ability for DevTools to wrap network transactions.

net/http/http_network_layer.h

Index: net/http/http_network_layer.h
diff --git a/net/http/http_network_layer.h b/net/http/http_network_layer.h
index fc94d0a7234b5f07a8e026a098414a5df77e82be..a3bbf0d6454b337f51169f71972af2f1f7c0d6fe 100644
--- a/net/http/http_network_layer.h
+++ b/net/http/http_network_layer.h
@@ -52,6 +52,21 @@ class NET_EXPORT HttpNetworkLayer
   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_;