Wire up an api to darken screen for accessibility

third_party/closure_compiler/externs/accessibility_private.js

Index: third_party/closure_compiler/externs/accessibility_private.js
diff --git a/third_party/closure_compiler/externs/accessibility_private.js b/third_party/closure_compiler/externs/accessibility_private.js
index 8bbd66c79d6ee67ef68072d08ecd11708c2cc04c..f4cf5d3ef1b0941e0c84041967cf8832a8f56df8 100644
--- a/third_party/closure_compiler/externs/accessibility_private.js
+++ b/third_party/closure_compiler/externs/accessibility_private.js
@@ -1,4 +1,4 @@
-// Copyright 2016 The Chromium Authors. All rights reserved.
+// Copyright 2017 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.
 
@@ -93,6 +93,13 @@ chrome.accessibilityPrivate.setFocusRing = function(rects) {};
 chrome.accessibilityPrivate.setKeyboardListener = function(enabled, capture) {};
 
 /**
+ * Darkens or undarkens the screen.
+ * @param {boolean} enabled True to darken screen; false to undarken screen.
+ * @see https://developer.chrome.com/extensions/accessibilityPrivate#method-darkenScreen
+ */
+chrome.accessibilityPrivate.darkenScreen = function(enabled) {};
+
+/**
  * Fired whenever ChromeVox should output introduction.
  * @type {!ChromeEvent}
  * @see https://developer.chrome.com/extensions/accessibilityPrivate#event-onIntroduceChromeVox