Allow the VR omnibox to be transient.

chrome/browser/resources/vr_shell/vr_shell_ui.css

 /* 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. */
 
 html {
   background-color: rgba(255, 255, 255, 0);
 }
 
 #ui {
   --scaleFactor: 4;
@@ skipping 121 matching lines @@
   transform: scaleX(-1);
 }
 
 #reload-ui-button {
   background-color: #555;
   color: white;
   font-size: 24px;
   padding: 12px;
 }
 
+#omni-container {
+  --tranX: 0;
+  --tranY: -0.65;
+  --tranZ: -1.2;
+}
+
 #omni {
-  --tranX: 0;
-  --tranY: -0.5;
-  --tranZ: -1.0;
   align-items: center;
   background-color: rgba(255, 255, 255, 0.9);
   border-radius: 100px;
   box-sizing: border-box;
   display: flex;
   height: 104px;
   justify-content: center;
   margin-bottom: 60px;
   margin-top: 0;
   opacity: 1;
-  transition: opacity 250ms ease, margin-top 250ms ease;
+  transition: opacity 500ms ease, margin-top 500ms ease;
   white-space: nowrap;
   width: 512px;
 }
 
 #omni-content {
   align-items: center;
   display: flex;
   max-width: 448px;
 }
 
@@ skipping 24 matching lines @@
   border: 4px solid rgb(86, 203, 255);
 }
 
 #omni.idle {
   background-color: #ececec;
 }
 
 #omni.idle #domain {
   color: black;
 }