Pull in vr_shell code for webvr

chrome/browser/android/vr_shell/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/android/rules.gni")
 import("//chrome/common/features.gni")
 import("//testing/test.gni")
 
-assert(enable_vr_shell && android_java_ui)
+assert((enable_vr_shell || enable_webvr) && android_java_ui)
 
 static_library("vr_shell") {
   sources = [
     "animation.cc",
     "animation.h",
     "easing.cc",
     "easing.h",
     "ui_elements.cc",
     "ui_elements.h",
     "ui_scene.cc",
@@ skipping 49 matching lines @@
   ]
 
   deps = [
     ":vr_shell",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//testing/gtest",
     "//ui/gfx/geometry",
   ]
 }