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

chrome/browser/extensions/updater/chrome_update_client_config.cc

Index: chrome/browser/extensions/updater/chrome_update_client_config.cc
diff --git a/chrome/browser/extensions/updater/chrome_update_client_config.cc b/chrome/browser/extensions/updater/chrome_update_client_config.cc
index feaedd1a5b8b9476752709ed3a35c1fd190fcc9c..3ae3dca6da0e4f14fa7f748d105acd4e86d97481 100644
--- a/chrome/browser/extensions/updater/chrome_update_client_config.cc
+++ b/chrome/browser/extensions/updater/chrome_update_client_config.cc
@@ -66,6 +66,10 @@ std::string ChromeUpdateClientConfig::ExtraRequestParams() const {
   return impl_.ExtraRequestParams();
 }
 
+std::string ChromeUpdateClientConfig::GetDownloadPreference() const {
+  return std::string();
+}
+
 net::URLRequestContextGetter* ChromeUpdateClientConfig::RequestContext() const {
   return impl_.RequestContext();
 }