Change how the VR reticle distance is determined.

chrome/browser/resources/vr_shell/vr_shell_ui_scene.js

 // 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.
 
 var scene = {};
 
 /**
  * The scene class assists in managing element and animations in the UI.  It
  * allows UI update API commands to be queued in batches, and manages allocation
  * of element and animation IDs.
@@ skipping 111 matching lines @@
    */
   removeAnimation(id) {
     // To-do: Make sure ID exists.
     this.commands.push({
       'type': api.Command.REMOVE_ANIMATION,
       'data': {'id': id, 'meshId': this.animations[id]}
     });
     delete this.animations[id];
   }
 
+  /**
+   * Set the background color of the scene.
+   * @param {{r: number, b: number, g: number, a: number}} color

[cjgrant, 2017/02/16 22:53:39]

Note that this works, for future reference.  If the UI's color parameters were
passed in as {a, b, c, x}, this will fail closure.

+   */
   setBackgroundColor(color) {
     this.commands.push(
         {'type': api.Command.UPDATE_BACKGROUND, 'data': {'color': color}});
   }
 
   /**
+   * Set the radius of background-bounding sphere.
+   * @param {number} distance
+   */
+  setBackgroundDistance(distance) {
+    this.commands.push({
+      'type': api.Command.UPDATE_BACKGROUND,
+      'data': {'distance': distance}
+    });
+  }
+  /**
    * Purge all elements in the scene.
    */
   purge() {
     var ids = Object.keys(this.animations);
     for (let id_key of ids) {
       var id = parseInt(id_key, 10);
       this.removeAnimation(id);
     }
     var ids = this.elements.values();
     for (let id of ids) {
       this.removeElement(id);
     }
     this.flush();
   }
 };