Implement Windows GPO support for "dlpref" in component updater.

components/update_client/update_checker.cc

Index: components/update_client/update_checker.cc
diff --git a/components/update_client/update_checker.cc b/components/update_client/update_checker.cc
index 2c8b888c3e3542a5a1aac16313695bdabeffe580..56de778d9c0efac5386f1b1a7c6447eae898dcbd 100644
--- a/components/update_client/update_checker.cc
+++ b/components/update_client/update_checker.cc
@@ -69,10 +69,10 @@ std::string BuildUpdateCheckRequest(const Configurator& config,
     VLOG(1) << "Appending to update request: " << app;
   }
 
-  return BuildProtocolRequest(config.GetBrowserVersion().GetString(),
-                              config.GetChannel(), config.GetLang(),
-                              config.GetOSLongName(), app_elements,
-                              additional_attributes);
+  return BuildProtocolRequest(
+      config.GetBrowserVersion().GetString(), config.GetChannel(),
+      config.GetLang(), config.GetOSLongName(), config.GetDownloadPreference(),
+      app_elements, additional_attributes);
 }
 
 class UpdateCheckerImpl : public UpdateChecker {