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

components/update_client/configurator.h

Index: components/update_client/configurator.h
diff --git a/components/update_client/configurator.h b/components/update_client/configurator.h
index 7f261c4b4d9435a5e2e6a6d638a863e5ff5243ac..5d6a16a48138ff26361d89997944c11bb6329e42 100644
--- a/components/update_client/configurator.h
+++ b/components/update_client/configurator.h
@@ -77,6 +77,12 @@ class Configurator : public base::RefCountedThreadSafe<Configurator> {
   // XML element.
   virtual std::string ExtraRequestParams() const = 0;
 
+  // Provides a hint for the server to control the order in which multiple
+  // download urls are returned. The hint may or may not be honored in the
+  // response returned by the server.
+  // Returns an empty string if no policy is in effect.
+  virtual std::string GetDownloadPreference() const = 0;
+
   // The source of contexts for all the url requests.
   virtual net::URLRequestContextGetter* RequestContext() const = 0;