Added data reduction proxy holdback experiment

components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc

Index: components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc
diff --git a/components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc b/components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc
index cc575c94c3f6ef5e5cabd93855ed99cb89d94dd7..3026d379f5ec6281ce734c43ad19ce65a2694333 100644
--- a/components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc
+++ b/components/data_reduction_proxy/browser/data_reduction_proxy_settings.cc
@@ -110,7 +110,6 @@ void DataReductionProxySettings::InitDataReductionProxySettings(
   url_request_context_getter_ = url_request_context_getter;
   InitPrefMembers();
   RecordDataReductionInit();
-
   // Disable the proxy if it is not allowed to be used.
   if (!params_->allowed())
     return;
@@ -356,7 +355,6 @@ void DataReductionProxySettings::MaybeActivateDataReductionProxy(
     prefs->SetBoolean(prefs::kDataReductionProxyWasEnabledBefore, true);
     ResetDataReductionStatistics();
   }
-
   // Configure use of the data reduction proxy if it is enabled.
   enabled_by_user_= IsDataReductionProxyEnabled();
   SetProxyConfigs(enabled_by_user_,
@@ -379,7 +377,7 @@ void DataReductionProxySettings::SetProxyConfigs(bool enabled,
   LogProxyState(enabled, restricted, at_startup);
   // The alternative is only configured if the standard configuration is
   // is enabled.
-  if (enabled) {
+  if (enabled & !params_->holdback()) {
     if (alternative_enabled) {
       configurator_->Enable(restricted,
                             !params_->fallback_allowed(),