Set exp id in the CP header if user is in Lo-Fi control.

components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
index 46a301c7b2e3b37f46648e05f6d12e0b75a60e19..86471b0a33db38fc7922906eceb78ae2aa29b38f 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
@@ -221,6 +221,10 @@ class DataReductionProxyConfig
   // Should be called on all URL requests (main frame and non main frame).
   bool ShouldUseLoFiHeaderForRequests() const;
 
+  // Returns true if the session is in the Lo-Fi control experiment. This
+  // happens if user is in Control group, and connection is slow.
+  bool IsInLoFiActiveControlExperiment() const;
+
   // Sets |lofi_status_| to LOFI_STATUS_OFF.
   void SetLoFiModeOff();