extensions: Relocate pref name constants.

chrome/browser/media_galleries/media_galleries_preferences.cc

Index: chrome/browser/media_galleries/media_galleries_preferences.cc
diff --git a/chrome/browser/media_galleries/media_galleries_preferences.cc b/chrome/browser/media_galleries/media_galleries_preferences.cc
index 786fb552191c64b4705b0068ae3d6ef4a971d43f..914223f4ea9cc1f3029cf092e2b6b449f2d0be5a 100644
--- a/chrome/browser/media_galleries/media_galleries_preferences.cc
+++ b/chrome/browser/media_galleries/media_galleries_preferences.cc
@@ -31,6 +31,7 @@
 #include "chrome/common/pref_names.h"
 #include "components/user_prefs/pref_registry_syncable.h"
 #include "content/public/browser/browser_thread.h"
+#include "extensions/browser/pref_names.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/extension_set.h"
 #include "extensions/common/permissions/api_permission.h"
@@ -1124,7 +1125,7 @@ void MediaGalleriesPreferences::RemoveGalleryPermissionsFromPrefs(
   DCHECK(IsInitialized());
   ExtensionPrefs* prefs = GetExtensionPrefs();
   const base::DictionaryValue* extensions =
-      prefs->pref_service()->GetDictionary(prefs::kExtensionsPref);
+      prefs->pref_service()->GetDictionary(extensions::pref_names::kExtensions);
   if (!extensions)
     return;