Enable accessible name of a control to include multiple <label> elements.

third_party/WebKit/Source/modules/accessibility/AXObject.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 730 matching lines @@
     AXObjectSet visited;
     AXNameFrom tmpNameFrom;
     AXRelatedObjectVector tmpRelatedObjects;
     String text = textAlternative(false, false, visited, tmpNameFrom, &tmpRelatedObjects, nameSources);
     text = text.simplifyWhiteSpace(isHTMLSpace<UChar>);
     return text;
 }
 
 String AXObject::recursiveTextAlternative(const AXObject& axObj, bool inAriaLabelledByTraversal, AXObjectSet& visited)
 {
+    if (visited.contains(&axObj) && !inAriaLabelledByTraversal)
+        return String();
+
     AXNameFrom tmpNameFrom;
     return axObj.textAlternative(true, inAriaLabelledByTraversal, visited, tmpNameFrom, nullptr, nullptr);
 }
 
 bool AXObject::isHiddenForTextAlternativeCalculation() const
 {
     if (equalIgnoringCase(getAttribute(aria_hiddenAttr), "false"))
         return false;
 
     if (getLayoutObject())
@@ skipping 34 matching lines @@
         if (nameSources) {
             nameSources->append(NameSource(*foundTextAlternative, attr));
             nameSources->last().type = nameFrom;
         }
 
         const AtomicString& ariaLabelledby = getAttribute(attr);
         if (!ariaLabelledby.isNull()) {
             if (nameSources)
                 nameSources->last().attributeValue = ariaLabelledby;
 
-            textAlternative = textFromAriaLabelledby(visited, relatedObjects);
-
+            // Operate on a copy of |visited| so that if |nameSources| is not null,
+            // the set of visited objects is preserved unmodified for future calculations.
+            AXObjectSet visitedCopy = visited;
+            textAlternative = textFromAriaLabelledby(visitedCopy, relatedObjects);
             if (!textAlternative.isNull()) {
                 if (nameSources) {
                     NameSource& source = nameSources->last();
                     source.type = nameFrom;
                     source.relatedObjects = *relatedObjects;
                     source.text = textAlternative;
                     *foundTextAlternative = true;
                 } else {
                     *foundTextAlternative = true;
                     return textAlternative;
@@ skipping 914 matching lines @@
 
 DEFINE_TRACE(AXObject)
 {
     visitor->trace(m_children);
     visitor->trace(m_parent);
     visitor->trace(m_cachedLiveRegionRoot);
     visitor->trace(m_axObjectCache);
 }
 
 } // namespace blink