Let prefetched resources skip cache revalidation once for a short duration.

net/http/http_transaction_test_util.h

Index: net/http/http_transaction_test_util.h
diff --git a/net/http/http_transaction_test_util.h b/net/http/http_transaction_test_util.h
index e6e831257e878a8b6d87083229ebab535db5ef7d..1459f2daaa6bcdb57a4b8ec78d925070c96dd989 100644
--- a/net/http/http_transaction_test_util.h
+++ b/net/http/http_transaction_test_util.h
@@ -291,11 +291,23 @@ class MockNetworkLayer : public net::HttpTransactionFactory,
   net::HttpCache* GetCache() override;
   net::HttpNetworkSession* GetSession() override;
 
+  // The caller must guarantee that |clock| will outlive this object.
+  void SetClock(base::Clock* clock);
+  base::Clock* clock() const { return clock_; }
+
  private:
   int transaction_count_;
   bool done_reading_called_;
   bool stop_caching_called_;
   net::RequestPriority last_create_transaction_priority_;
+
+  scoped_ptr<base::Clock> default_clock_;
+
+  // Normally clock_ points to default_clock_ but it can be overridden to point
+  // to a custom
+  // clock set by test_clock().
+  base::Clock* clock_;
+
   base::WeakPtr<MockNetworkTransaction> last_transaction_;
 };