Add a group policy controlling which sites can install extensions.

chrome/common/pref_names.h

 // Copyright (c) 2012 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 #pragma once
 
@@ skipping 473 matching lines @@
 
 extern const char kDisableVideoAndChat[];
 
 extern const char kDisableExtensions[];
 extern const char kDisablePluginFinder[];
 extern const char kBrowserActionContainerWidth[];
 
 extern const char kLastExtensionsUpdateCheck[];
 extern const char kNextExtensionsUpdateCheck[];
 
+extern const char kExtensionAllowedInstallSites[];
 extern const char kExtensionInstallAllowList[];
 extern const char kExtensionInstallDenyList[];
-
 extern const char kExtensionAlertsInitializedPref[];
-
 extern const char kExtensionInstallForceList[];
-
 extern const char kExtensionBlacklistUpdateVersion[];
 
 extern const char kNtpTipsResourceServer[];
 
 extern const char kNtp4IntroDisplayCount[];
 extern const char kNtpCollapsedForeignSessions[];
 extern const char kNtpMostVisitedURLsBlacklist[];
 extern const char kNtpPromoResourceCache[];
 extern const char kNtpPromoResourceCacheUpdate[];
 extern const char kNtpPromoResourceServer[];
@@ skipping 209 matching lines @@
 #endif
 
 extern const char kInManagedMode[];
 
 extern const char kNetworkProfileWarningsLeft[];
 extern const char kNetworkProfileLastWarningTime[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_