Do not request Data Reduction Proxy configuration if disabled.

A minor tweak to disable retrieving a Data Reduction Proxy configuration
from the config service if the feature is not enabled by the user, but
the config service is enabled.

Review URL: https://codereview.chromium.org/1166803004

Cr-Commit-Position: refs/heads/master@{#333175}

components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc

@@ -213,7 +213,8 @@ void DataReductionProxySettings::UpdateIOData(bool at_startup) {
   data_reduction_proxy_service_->SetProxyPrefs(
       IsDataReductionProxyEnabled(), IsDataReductionProxyAlternativeEnabled(),
       at_startup);
-  data_reduction_proxy_service_->RetrieveConfig();
+  if (IsDataReductionProxyEnabled())
+    data_reduction_proxy_service_->RetrieveConfig();
 }
 
 void DataReductionProxySettings::MaybeActivateDataReductionProxy(