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

chrome/browser/extensions/updater/chrome_update_client_config.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_UPDATER_CHROME_UPDATE_CLIENT_CONFIG_H_
 #define CHROME_BROWSER_EXTENSIONS_UPDATER_CHROME_UPDATE_CLIENT_CONFIG_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 17 matching lines @@
   int StepDelay() const override;
   int OnDemandDelay() const override;
   int UpdateDelay() const override;
   std::vector<GURL> UpdateUrl() const override;
   std::vector<GURL> PingUrl() const override;
   base::Version GetBrowserVersion() const override;
   std::string GetChannel() const override;
   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;
   bool DeltasEnabled() const override;
   bool UseBackgroundDownloader() const override;
 
  protected:
   friend class base::RefCountedThreadSafe<ChromeUpdateClientConfig>;
   ~ChromeUpdateClientConfig() override;
 
  private:
   component_updater::ConfiguratorImpl impl_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeUpdateClientConfig);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_UPDATER_CHROME_UPDATE_CLIENT_CONFIG_H_