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..677172bc1f7b39ab4eac1ae3e8d9e1d6e78c2065 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 Lo-Fi control experiment. This happens

[bengr, 2015/10/02 19:34:29]

// Returns true if the session is in the control group of the Lo-Fi experiment
and Lo-Fi mode is activated.

+  // if user is in Control group, and connection is slow.
+  bool IsInLoFiControlExperiment() const;

[bengr, 2015/10/02 19:34:29]

I don't like the name, probably because I don't like the function because it
combines concerns. I think there should be two methods:
IsInLoFiExperimentControlGroup() and
IsLofiActive()

[tbansal1, 2015/10/02 20:28:38]

It will be:
IsInLoFiControlFieldTrial() && IsLofiActive() && !IsLofiActiveViaFlags()

I thought it would be better to keep this logic within config.cc, and not spread
it out to different files. wdyt?

+
   // Sets |lofi_status_| to LOFI_STATUS_OFF.
   void SetLoFiModeOff();