Introduce a delegate to avoid hardcoding "chrome-extension" in net/.

net/url_request/url_request_test_util.h

Index: net/url_request/url_request_test_util.h
diff --git a/net/url_request/url_request_test_util.h b/net/url_request/url_request_test_util.h
index 26ce942f73d008357f48a7643e8945a8a71e044c..90a074b5a32847bc7b19b9e96550027857dc8e8f 100644
--- a/net/url_request/url_request_test_util.h
+++ b/net/url_request/url_request_test_util.h
@@ -244,6 +244,8 @@ class TestNetworkDelegate : public net::NetworkDelegate {
                               net::CookieOptions* options) OVERRIDE;
   virtual bool OnCanAccessFile(const net::URLRequest& request,
                                const FilePath& path) const OVERRIDE;
+  virtual bool OnCanThrottleRequest(
+      const net::URLRequest& request) const OVERRIDE;
 
   void InitRequestStatesIfNew(int request_id);