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.automation.getDesktop(function(desktop) {
+        desktop.toggleDarkenScreen(false);

[dmazzoni, 2017/03/22 21:40:48]

Why call it twice?

[David Tseng, 2017/03/22 22:51:38]

The other end of the dbus message is sticky. So, if you turned backlights off in
the past and adjusted brightness, the force backlights flag is still off, but
the screen is on. To get back to a known state, we need to clear the previous
state.

+        desktop.toggleDarkenScreen(true);
+      });
+      new Output().format('@darken_screen').go();
+      break;
+    case 'undarkenScreen':
+      chrome.automation.getDesktop(function(desktop) {
+        desktop.toggleDarkenScreen(true);
+        desktop.toggleDarkenScreen(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