Add chrome://vr-shell-ui internal page

chrome/browser/resources/vr_shell/vr_shell_ui.css

Index: chrome/browser/resources/vr_shell/vr_shell_ui.css
diff --git a/chrome/browser/resources/cast/cast.css b/chrome/browser/resources/vr_shell/vr_shell_ui.css
similarity index 55%
copy from chrome/browser/resources/cast/cast.css
copy to chrome/browser/resources/vr_shell/vr_shell_ui.css
index 5193f40523bfa2e99df63fc8f271dd48d38e11f1..66774d091860eec3fe86b0e2e71ecba881c330a4 100644
--- a/chrome/browser/resources/cast/cast.css
+++ b/chrome/browser/resources/vr_shell/vr_shell_ui.css
@@ -2,17 +2,16 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
-body,
-extensionview,
-html  {
-  border: 0;
-  height: 100%;
-  margin: 0;
-  padding: 0;
-  width: 100%;
+html {
+  background-color: rgba(255, 255, 255, 0.2);
+  font-size: 20px;
 }
 
-extensionview {
+.ui-button {
+  background: white;
+  border-radius: 6px;
   overflow: hidden;
   position: absolute;
+  text-align: center;
+  vertical-align: middle;
 }