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

chrome/browser/extensions/updater/chrome_update_client_config.h

Index: chrome/browser/extensions/updater/chrome_update_client_config.h
diff --git a/chrome/browser/extensions/updater/chrome_update_client_config.h b/chrome/browser/extensions/updater/chrome_update_client_config.h
index 5f7ab3b0757edf3d4256505ba1a871f513fdafa0..7e6b020758e915f8c38edf7dbf2837d4de446046 100644
--- a/chrome/browser/extensions/updater/chrome_update_client_config.h
+++ b/chrome/browser/extensions/updater/chrome_update_client_config.h
@@ -35,6 +35,7 @@ class ChromeUpdateClientConfig : public UpdateClientConfig {
   std::string GetLang() const override;
   std::string GetOSLongName() const override;
   std::string ExtraRequestParams() const override;
+  std::string GetDownloadPreference() const override;
   net::URLRequestContextGetter* RequestContext() const override;
   scoped_refptr<update_client::OutOfProcessPatcher> CreateOutOfProcessPatcher()
       const override;