Add the enable_polymer_v08 flag for gn. Equivalent gyp change was

build/config/features.gni

 # Copyright 2014 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.
 
 # This file contains UI-related build flags. It should theoretically be in the
 # src/ui directory and only things that depend on the ui module should get the
 # definitions.
 #
 # However, today we have many "bad" dependencies on some of these flags from,
 # e.g. base, so they need to be global.
@@ skipping 61 matching lines @@
   enable_supervised_users = !is_ios
 
   enable_autofill_dialog = !is_ios
 
   enable_google_now = !is_ios && !is_android
 
   enable_one_click_signin = is_win || is_mac || (is_linux && !is_chromeos)
 
   enable_remoting = !is_ios && !is_android
 
+  # Enable to include Polymer 0.8 in the binary.
+  enable_polymer_v08 = false
+
   # Enable hole punching for the protected video.
   enable_video_hole = is_android
 
   # Enables browser side Content Decryption Modules. Required for embedders
   # (e.g. Android and ChromeCast) that use a browser side CDM.
   enable_browser_cdms = is_android
 }
 
 # Additional dependent variables -----------------------------------------------
 
@@ skipping 91 matching lines @@
 # TODO(GYP) also require !embedded to enable.
 use_gconf = is_linux && !is_chromeos
 
 # Hangout services is an extension that adds extra features to Hangouts.
 # For official GYP builds, this flag is set, it will likely need to be
 # parameterized in the future for a similar use.
 enable_hangout_services_extension = false
 
 # Whether to back up data before sync.
 enable_pre_sync_backup = is_win || is_mac || (is_linux && !is_chromeos)