Remove enable_webvr from build/config, and move it to the buildflag_header system.

chrome/common/features.gni

 # Copyright 2015 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/features.gni")
+import("//device/vr/features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//net/features.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
 import("//ui/base/ui_features.gni")
 
 # Please keep features in alphabetical order.
 declare_args() {
   enable_app_list = is_chromeos
@@ skipping 72 matching lines @@
   "enable_plugins=$enable_plugins",
   "enable_print_preview=$enable_print_preview",
   "enable_printing=$_enable_printing",
   "enable_service_discovery=$enable_service_discovery",
   "enable_webrtc=$enable_webrtc",
   "enable_webvr=$enable_webvr",
   "mac_views_browser=$mac_views_browser",
   "safe_browsing_mode=$safe_browsing_mode",
   "use_vulcanize=$use_vulcanize",
 ]