Wire up an api to darken screen for accessibility

content/renderer/accessibility/render_accessibility_impl.cc

 // Copyright (c) 2012 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.
 
 #include "content/renderer/accessibility/render_accessibility_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <queue>
@@ skipping 497 matching lines @@
       target.setSequentialFocusNavigationStartingPoint();
       break;
     case ui::AX_ACTION_SET_VALUE:
       target.setValue(blink::WebString::fromUTF16(data.value));
       HandleAXEvent(target, ui::AX_EVENT_VALUE_CHANGED);
       break;
     case ui::AX_ACTION_SHOW_CONTEXT_MENU:
       target.showContextMenu();
       break;
     case ui::AX_ACTION_REPLACE_SELECTED_TEXT:
+    case ui::AX_ACTION_TOGGLE_DARKEN_SCREEN:
     case ui::AX_ACTION_NONE:
       NOTREACHED();
       break;
   }
 }
 
 void RenderAccessibilityImpl::OnEventsAck(int ack_token) {
   // Ignore acks intended for a different or previous instance.
   if (ack_token_ != ack_token)
     return;
@@ skipping 138 matching lines @@
 
   const WebDocument& document = GetMainDocument();
   if (document.isNull())
     return;
 
   document.accessibilityObject().scrollToMakeVisibleWithSubFocus(
       WebRect(bounds.x(), bounds.y(), bounds.width(), bounds.height()));
 }
 
 }  // namespace content