[Devtools] Accessibility pane: correctly show label text source

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

 /*
  * Copyright (C) 2012, Google 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 2241 matching lines @@
       nameSources->back().nativeSource = AXTextFromNativeHTMLLabel;
     }
 
     LabelsNodeList* labels = toLabelableElement(htmlElement)->labels();
     if (labels && labels->length() > 0) {
       HeapVector<Member<Element>> labelElements;
       for (unsigned labelIndex = 0; labelIndex < labels->length();
            ++labelIndex) {
         Element* label = labels->item(labelIndex);
         if (nameSources) {
-          if (label->getAttribute(forAttr) == htmlElement->getIdAttribute())
+          if (!label->getAttribute(forAttr).isEmpty() &&
+              label->getAttribute(forAttr) == htmlElement->getIdAttribute()) {
             nameSources->back().nativeSource = AXTextFromNativeHTMLLabelFor;
-          else
+          } else {
             nameSources->back().nativeSource = AXTextFromNativeHTMLLabelWrapped;
+          }
         }
         labelElements.push_back(label);
       }
 
       textAlternative =
           textFromElements(false, visited, labelElements, relatedObjects);
       if (!textAlternative.isNull()) {
         *foundTextAlternative = true;
         if (nameSources) {
           NameSource& source = nameSources->back();
@@ skipping 619 matching lines @@
     return String();
   return toTextControlElement(node)->strippedPlaceholder();
 }
 
 DEFINE_TRACE(AXNodeObject) {
   visitor->trace(m_node);
   AXObject::trace(visitor);
 }
 
 }  // namespace blink