Add MacRTL feature to flags

chrome/browser/flag_descriptions.cc

 // Copyright 2017 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.
 
 #include "chrome/browser/flag_descriptions.h"
 
 namespace flag_descriptions {
 
 //  Material Design version of chrome://bookmarks
 
@@ skipping 3149 matching lines @@
     "Use the local New Tab page if Google is the default search engine.";
 
 const char kOneGoogleBarOnLocalNtpName[] =
     "Enable the OneGoogleBar on the local NTP";
 const char kOneGoogleBarOnLocalNtpDescription[] =
     "Show a OneGoogleBar on the local New Tab page if Google is the default "
     "search engine.";
 
 #endif  // !defined(OS_ANDROID) && !defined(OS_IOS)
 
+#if defined(OS_MACOSX)
+extern const char kMacRTLName[] = "Enable RTL";
+extern const char kMacRTLDescription[] =
+    "Mirrors the UI for RTL language users";
+#endif
+
 }  // namespace flag_descriptions