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

components/component_updater/configurator_impl.cc

Index: components/component_updater/configurator_impl.cc
diff --git a/components/component_updater/configurator_impl.cc b/components/component_updater/configurator_impl.cc
index 407da85963535e8b92165663e5404ab45f0d8f5c..e4c306907c06852a128b03aba586d4745a70dffa 100644
--- a/components/component_updater/configurator_impl.cc
+++ b/components/component_updater/configurator_impl.cc
@@ -182,6 +182,10 @@ std::string ConfiguratorImpl::ExtraRequestParams() const {
   return extra_info_;
 }
 
+std::string ConfiguratorImpl::GetDownloadPreference() const {
+  return std::string();
+}
+
 net::URLRequestContextGetter* ConfiguratorImpl::RequestContext() const {
   return url_request_getter_;
 }