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

device/vr/BUILD.gn

 # Copyright 2016 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/features.gni")
+import("features.gni")
+import("//build/buildflag_header.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")  # For generate_jni().
 }
 
+# Generate a buildflag header for compile-time checking of WebVR support.
+buildflag_header("features") {
+  header = "features.h"
+  flags = [ "ENABLE_WEBVR=$enable_webvr" ]
+}
+
 component("vr") {
   output_name = "device_vr"
 
   sources = [
     "vr_export.h",
   ]
   defines = [ "DEVICE_VR_IMPLEMENTATION" ]
   deps = [
     ":mojo_bindings",
   ]
@@ skipping 79 matching lines @@
 
   public_deps = [
     "//gpu/ipc/common:interfaces",
     "//mojo/common:common_custom_types",
   ]
 
   export_class_attribute = "DEVICE_VR_EXPORT"
   export_define = "DEVICE_VR_IMPLEMENTATION=1"
   export_header = "device/vr/vr_export.h"
 }