Deprecate direct use of legacy extension management preference

extensions/browser/extension_prefs.h

Index: extensions/browser/extension_prefs.h
diff --git a/extensions/browser/extension_prefs.h b/extensions/browser/extension_prefs.h
index 4b95e556939f90fe12ec699933971c66b0d8df23..a322e8a5d1d86b1ac4e7b36ffd8bf6f736d84b14 100644
--- a/extensions/browser/extension_prefs.h
+++ b/extensions/browser/extension_prefs.h
@@ -529,10 +529,6 @@ class ExtensionPrefs : public ExtensionScopedPrefs, public KeyedService {
   // The underlying AppSorting.
   AppSorting* app_sorting() const { return app_sorting_.get(); }
 
-  // Describes the URLs that are able to install extensions. See
-  // pref_names::kAllowedInstallSites for more information.
-  URLPatternSet GetAllowedInstallSites();
-
   // Schedules garbage collection of an extension's on-disk data on the next
   // start of this ExtensionService. Applies only to extensions with isolated
   // storage.