Ignore <rt> children when determining WebVTT text direction (LTR/RTL)

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

 /*
  * Copyright (c) 2013, Opera Software ASA. 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 508 matching lines @@
 {
     TextRun run(value);
     BidiResolver<VTTTextRunIterator, BidiCharacterRun> bidiResolver;
     bidiResolver.setStatus(BidiStatus(LTR, false));
     bidiResolver.setPositionIgnoringNestedIsolates(VTTTextRunIterator(&run, 0));
     return bidiResolver.determineParagraphDirectionality(&hasStrongDirectionality);
 }
 
 static CSSValueID determineTextDirection(DocumentFragment* vttRoot)
 {
-    DEFINE_STATIC_LOCAL(const String, rtTag, ("rt"));
     ASSERT(vttRoot);
 
     // Apply the Unicode Bidirectional Algorithm's Paragraph Level steps to the
     // concatenation of the values of each WebVTT Text Object in nodes, in a
     // pre-order, depth-first traversal, excluding WebVTT Ruby Text Objects and
     // their descendants.
     TextDirection textDirection = LTR;
-    for (Node& node : NodeTraversal::descendantsOf(*vttRoot)) {
-        if (!node.isTextNode() || node.localName() == rtTag)
-            continue;
+    Node* node = NodeTraversal::next(*vttRoot);
+    while (node) {
+        ASSERT(node->isDescendantOf(vttRoot));
 
-        bool hasStrongDirectionality;
-        textDirection = determineDirectionality(node.nodeValue(), hasStrongDirectionality);
-        if (hasStrongDirectionality)
-            break;
+        if (node->isTextNode()) {
+            bool hasStrongDirectionality;
+            textDirection = determineDirectionality(node->nodeValue(), hasStrongDirectionality);
+            if (hasStrongDirectionality)
+                break;
+        } else if (node->isVTTElement()) {
+            if (toVTTElement(node)->webVTTNodeType() == VTTNodeTypeRubyText) {
+                node = NodeTraversal::nextSkippingChildren(*node);
+                continue;
+            }
+        }
+
+        node = NodeTraversal::next(*node);
     }
     return isLeftToRightDirection(textDirection) ? CSSValueLtr : CSSValueRtl;
 }
 
 void VTTCue::calculateDisplayParameters()
 {
     createVTTNodeTree();
 
     // Steps 10.2, 10.3
     m_displayDirection = determineTextDirection(m_vttNodeTree.get());
@@ skipping 542 matching lines @@
 
 void VTTCue::trace(Visitor* visitor)
 {
     visitor->trace(m_vttNodeTree);
     visitor->trace(m_cueBackgroundBox);
     visitor->trace(m_displayTree);
     TextTrackCue::trace(visitor);
 }
 
 } // namespace blink