GN: Set |enable_webvr| in the declare_args() block.

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 Chrome-feature-related build flags (see ui.gni for
 # UI-related ones). These should theoretically be moved to the build files of
 # the features themselves.
 #
 # However, today we have many "bad" dependencies on some of these flags from,
 # e.g. base, so they need to be global to match the GYP configuration. Also,
@@ skipping 100 matching lines @@
 
   # Enable basic printing support and UI.
   enable_basic_printing = !is_chromecast && !is_ios
 
   # Enable printing with print preview. It does not imply
   # enable_basic_printing. It's possible to build Chrome with preview only.
   enable_print_preview = !is_android && !is_chromecast && !is_ios
 
   # Whether or not to use external popup menu.
   use_external_popup_menu = is_android || is_mac
+
+  # Enable WebVR support by default on Android
+  # Still requires command line flag to access API
+  enable_webvr = is_android
 }
 
 # Additional dependent variables -----------------------------------------------
 
 # Enable the spell checker.
 enable_spellcheck = !is_ios
 
 # Use the operating system's spellchecker rather than hunspell.
 use_browser_spellchecker = is_android || is_mac
 
@@ skipping 32 matching lines @@
 # Image loader extension is enabled on ChromeOS only.
 enable_image_loader_extension = is_chromeos
 
 # Chrome OS: whether to also build the upcoming version of
 # ChromeVox, which can then be enabled via a command-line switch.
 enable_chromevox_next = false
 
 # Use brlapi from brltty for braille display support.
 use_brlapi = is_chromeos
 
-# Enable WebVR support by default on Android
-# Still requires command line flag to access API
-enable_webvr = is_android
-
 enable_configuration_policy = !is_ios
 
 enable_mac_keystone = is_mac && is_chrome_branded && is_official_build
 enable_mac_crash_collection = is_mac && is_chrome_branded && is_official_build