Fix tag closing issues in the WebVTT tree builder

Source/core/html/track/vtt/VTTParser.cpp

 /*
  * Copyright (C) 2011 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 547 matching lines @@
             }
             if (!m_languageStack.isEmpty())
                 child->setLanguage(m_languageStack.last());
             m_currentNode->parserAppendChild(child);
             m_currentNode = child;
         }
         break;
     }
     case VTTTokenTypes::EndTag: {
         VTTNodeType nodeType = tokenToNodeType(m_token);
-        if (nodeType != VTTNodeTypeNone) {
-            if (nodeType == VTTNodeTypeLanguage && m_currentNode->isVTTElement() && toVTTElement(m_currentNode.get())->webVTTNodeType() == VTTNodeTypeLanguage)
-                m_languageStack.removeLast();
-            if (m_currentNode->parentNode())
-                m_currentNode = m_currentNode->parentNode();
+        if (nodeType == VTTNodeTypeNone)
+            break;
+
+        // The only non-VTTElement would be the DocumentFragment root. (Text
+        // nodes and PIs will never appear as m_currentNode.)
+        if (!m_currentNode->isVTTElement())
+            break;
+
+        VTTNodeType currentType = toVTTElement(m_currentNode.get())->webVTTNodeType();
+        bool matchesCurrent = nodeType == currentType;
+        if (!matchesCurrent) {
+            // </ruby> auto-closes <rt>.
+            if (currentType == VTTNodeTypeRubyText && nodeType == VTTNodeTypeRuby) {
+                if (m_currentNode->parentNode())
+                    m_currentNode = m_currentNode->parentNode();
+            } else {
+                break;
+            }
         }
+        if (nodeType == VTTNodeTypeLanguage)
+            m_languageStack.removeLast();
+        if (m_currentNode->parentNode())
+            m_currentNode = m_currentNode->parentNode();
         break;
     }
     case VTTTokenTypes::TimestampTag: {
         unsigned position = 0;
         String charactersString = m_token.characters();
         double time = VTTParser::collectTimeStamp(charactersString, &position);
         if (time != malformedTime)
             m_currentNode->parserAppendChild(ProcessingInstruction::create(document, "timestamp", charactersString));
         break;
     }
     default:
         break;
     }
 }
 
 void VTTParser::skipWhiteSpace(const String& line, unsigned* position)
 {
     while (*position < line.length() && isASpace(line[*position]))
         (*position)++;
 }
 
 }