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

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 842be0120794dc72f1a79ddba416325620f14516..d86f9ef8145f82f87fd1c8127264da549c85e196 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -10,6 +10,7 @@ import("//build/split_static_library.gni")
 import("//chrome/common/features.gni")
 import("//components/os_crypt/features.gni")
 import("//components/spellcheck/spellcheck_build_features.gni")
+import("//device/vr/features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//net/features.gni")
@@ -1558,6 +1559,7 @@ split_static_library("browser") {
     "//device/power_save_blocker",
     "//device/usb/mojo",
     "//device/usb/public/interfaces",
+    "//device/vr:features",
     "//extensions/features",
     "//gin:gin_features",
     "//google_apis",