Handles aria-dropeffect after getting its value from blink.

content/browser/accessibility/accessibility_tree_formatter_mac.mm

 // 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/browser/accessibility/accessibility_tree_formatter.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
@@ skipping 144 matching lines @@
       NSAccessibilityHelpAttribute,
       @"AXInvalid",
       NSAccessibilityDisclosingAttribute,
       NSAccessibilityDisclosureLevelAttribute,
       @"AXAccessKey",
       @"AXARIAAtomic",
       @"AXARIABusy",
       @"AXARIALive",
       @"AXARIARelevant",
       NSAccessibilityColumnIndexRangeAttribute,
+      @"AXDropEffects",
       NSAccessibilityEnabledAttribute,
       NSAccessibilityExpandedAttribute,
       NSAccessibilityFocusedAttribute,
       @"AXGrabbed",
       NSAccessibilityIndexAttribute,
       @"AXLoaded",
       @"AXLoadingProcess",
       NSAccessibilityNumberOfCharactersAttribute,
       NSAccessibilityOrientationAttribute,
       @"AXPlaceholder",
@@ skipping 136 matching lines @@
 const string AccessibilityTreeFormatter::GetAllowString() {
   return "@MAC-ALLOW:";
 }
 
 // static
 const string AccessibilityTreeFormatter::GetDenyString() {
   return "@MAC-DENY:";
 }
 
 }  // namespace content