Add way to get native VR UI information from Java

chrome/browser/resources/vr_shell/vr_shell_ui.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 vrShellUi = (function() {
   'use strict';
 
   let ui = new scene.Scene();
   let uiManager;
   let nativeCommandHandler;
 
   let uiRootElement = document.querySelector('#ui');
   let uiStyle = window.getComputedStyle(uiRootElement);
   /** @const */ var ANIM_DURATION = 150;
 
   // This value should match the one in VrShellImpl.java
   /** @const */ var UI_DPR = 1.2;
 
+  var domIdToUiElementIdMap = {};
+
   function getStyleFloat(style, property, defaultValue) {
     let value = parseFloat(style.getPropertyValue(property));
     return isNaN(value) ? defaultValue : value;
   }
 
   function getStyleString(style, property) {
     let str = style.getPropertyValue(property);
     return !str || 0 === str.length ? '' : str;
   }
 
   // Generate a two-color progress bar style background using a gradient.
   function makeProgressBackground(loading, percentage, color, background) {
     if (!loading) {
       return background;
     }
     return 'linear-gradient(to right, ' + color + ' 0%, ' + color + ' ' +
         percentage * 100.0 + '%, ' + background + ' ' + percentage * 100 +
         '%, ' + background + ' 100%)';
   }
 
+  function getUiElementId(domId) {
+    return domId in domIdToUiElementIdMap ? domIdToUiElementIdMap[domId] : -1;
+  }
+
   class ContentQuad {
     constructor() {
       /** @const */ this.SCREEN_HEIGHT = 1.375;
       /** @const */ this.SCREEN_RATIO = 9.6 / 6.4;
       /** @const */ this.BROWSING_SCREEN_ELEVATION = -0.15;
       /** @const */ this.BROWSING_SCREEN_DISTANCE = 2.0;
       /** @const */ this.FULLSCREEN_DISTANCE = 3.0;
       /** @const */ this.CSS_WIDTH_PIXELS = 960.0;
       /** @const */ this.CSS_HEIGHT_PIXELS = 640.0;
       /** @const */ this.DPR = 1.2;
@@ skipping 150 matching lines @@
       this.rotationX = getStyleFloat(style, '--rotX', 0);
       this.rotationY = getStyleFloat(style, '--rotY', 0);
       this.rotationZ = getStyleFloat(style, '--rotZ', 0);
       if (this.rotationX != 0 || this.rotationY != 0 || this.rotationZ != 0) {
         element.setRotation(
             this.rotationX, this.rotationY, this.rotationZ, 2 * Math.PI);
       }
 
       this.id = ui.addElement(element);
       this.domElement = domElement;
+      domIdToUiElementIdMap[domId] = this.id;

[tiborg, 2017/03/27 15:14:33]

cjgrant@: is this a good workaround until the names exist?

[cjgrant, 2017/03/27 15:41:32]

Brian said he'd wait on using element names, as that patch will land soon. 
Personally I'd prefer not to have this particular map, but either way, we will
need a "name to element" map.

[bsheedy, 2017/03/27 17:49:09]

Do we really need a map since we're removing all the JS from this CL once your
patch lands? On the native side, GetUiElementById just uses a linear search, so
I imagine GetUiElementByName will do the same.

[cjgrant, 2017/03/27 19:49:43]

That works if test will only ever check native state.  I can't imagine that
being the case though.  I picture tests checking a mix of native and Javascript
state, depending on what exactly you're testing.  But as always, I guess we add
what we need, when we need it.

[tiborg, 2017/03/27 19:59:59]

+1 to add the map once we need it.

     }
   };
 
   class Button {
     constructor(domId, callback, parentId) {
       let captionId = domId + '-caption';
       this.button = document.querySelector(domId);
       this.caption = document.querySelector(captionId);
       this.callback = callback;
       this.enabled = true;
@@ skipping 1113 matching lines @@
     }
   }
 
   function command(dict) {
     nativeCommandHandler.handleCommand(dict);
   }
 
   return {
     initialize: initialize,
     command: command,
+    getUiElementId: getUiElementId,
   };
 })();
 
 window.addEventListener('load', vrShellUi.initialize);