DataReductionProxyNetworkDelegate::OnBeforeSendProxyHeadersInternal is only called in the case where a proxy is being used (see HttpNetworkTransaction::UsingHttpProxyWithoutTunnel). The NetworkDelegate should explicitly check if the proxy_server in proxy_info is a DataReductionProxy, and it should not run any code in the case that is not a DataReductionProxy.

Any code that needs to run in either case should be called in OnBeforeSendHeadersInternal. If this is not possible due to timing (SetLoFiModeActiveOnMainFrame might need to be called in either case), the lofi bool added to DataReductionProxyData in URLRequest's UserData can be used to make an evaluation in OnSendHeadersInternal.