Wire up an api to darken screen for accessibility

chrome/browser/resources/chromeos/chromevox/cvox2/background/command_handler.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.
 
 /**
  * @fileoverview ChromeVox commands.
  */
 
 goog.provide('CommandHandler');
 
@@ skipping 174 matching lines @@
         ChromeVoxState.instance.navigateToRange(
             ChromeVoxState.instance.currentRange);
       }
       break;
     case 'help':
       (new PanelCommand(PanelCommandType.TUTORIAL)).send();
       return false;
     case 'showNextUpdatePage':
       (new PanelCommand(PanelCommandType.UPDATE_NOTES)).send();
       return false;
+    case 'darkenScreen':
+      chrome.accessibilityPrivate.darkenScreen(true);
+      new Output().format('@darken_screen').go();
+      break;
+    case 'undarkenScreen':
+      chrome.accessibilityPrivate.darkenScreen(false);
+      new Output().format('@undarken_screen').go();
+      break;
     default:
       break;
   }
 
   // Require a current range.
   if (!ChromeVoxState.instance.currentRange_)
     return true;
 
   // Next/classic compat commands hereafter.
   if (ChromeVoxState.instance.mode == ChromeVoxMode.CLASSIC)
@@ skipping 631 matching lines @@
   if (imageNode.imageDataUrl) {
     var event = new CustomAutomationEvent(
         EventType.IMAGE_FRAME_UPDATED, imageNode, 'page');
     CommandHandler.onImageFrameUpdated_(event);
   } else {
     imageNode.getImageData(0, 0);
   }
 };
 
 }); //  goog.scope