Fix accessibility constant clash in OSX 10.12.

content/browser/accessibility/browser_accessibility_cocoa.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 <execinfo.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #import "content/browser/accessibility/browser_accessibility_cocoa.h"
 
@@ skipping 35 matching lines @@
 NSString* const NSAccessibilityARIAPosInSetAttribute = @"AXARIAPosInSet";
 NSString* const NSAccessibilityARIARelevantAttribute = @"AXARIARelevant";
 NSString* const NSAccessibilityARIASetSizeAttribute = @"AXARIASetSize";
 NSString* const NSAccessibilityAccessKeyAttribute = @"AXAccessKey";
 NSString* const NSAccessibilityDropEffectsAttribute = @"AXDropEffects";
 NSString* const NSAccessibilityGrabbedAttribute = @"AXGrabbed";
 NSString* const NSAccessibilityInvalidAttribute = @"AXInvalid";
 NSString* const NSAccessibilityIsMultiSelectableAttribute =
     @"AXIsMultiSelectable";
 NSString* const NSAccessibilityLoadingProgressAttribute = @"AXLoadingProgress";
-NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";
 NSString* const
     NSAccessibilityUIElementCountForSearchPredicateParameterizedAttribute =
         @"AXUIElementCountForSearchPredicate";
 NSString* const
     NSAccessibilityUIElementsForSearchPredicateParameterizedAttribute =
         @"AXUIElementsForSearchPredicate";
 NSString* const NSAccessibilityVisitedAttribute = @"AXVisited";
 
 // Private attributes for text markers.
 NSString* const NSAccessibilityStartTextMarkerAttribute = @"AXStartTextMarker";
@@ skipping 430 matching lines @@
           search->AddPredicate(predicate);
       }
     }
   }
 
   return true;
 }
 
 }  // namespace
 
+// The following private WebKit accessibility attribute became public in 10.12.
+#if !defined(MAC_OS_X_VERSION_10_12) || \
+    MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12
+extern "C" {
+NSString* const NSAccessibilityRequiredAttribute = @"AXRequired";
+}
+#endif  // MAC_OS_X_VERSION_10_12
+
 @implementation BrowserAccessibilityCocoa
 
 + (void)initialize {
   const struct {
     NSString* attribute;
     NSString* methodName;
   } attributeToMethodNameContainer[] = {
       {NSAccessibilityARIAAtomicAttribute, @"ariaAtomic"},
       {NSAccessibilityARIABusyAttribute, @"ariaBusy"},
       {NSAccessibilityARIALiveAttribute, @"ariaLive"},
@@ skipping 2334 matching lines @@
   if (![self instanceActive])
     return [super hash];
   return browserAccessibility_->GetId();
 }
 
 - (BOOL)accessibilityShouldUseUniqueId {
   return YES;
 }
 
 @end