Revert of Simplify LoadableTextTrack::trackElementIndex

third_party/WebKit/Source/core/html/track/LoadableTextTrack.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:
  * 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 17 matching lines @@
 #include "core/dom/ElementTraversal.h"
 #include "core/html/HTMLTrackElement.h"
 #include "core/html/track/vtt/VTTRegionList.h"
 
 namespace blink {
 
 LoadableTextTrack::LoadableTextTrack(HTMLTrackElement* track)
     : TextTrack(subtitlesKeyword(), emptyAtom, emptyAtom, emptyAtom, TrackElement)
     , m_trackElement(track)
 {
-    DCHECK(m_trackElement);
 }
 
 LoadableTextTrack::~LoadableTextTrack()
 {
 }
 
 bool LoadableTextTrack::isDefault() const
 {
+    ASSERT(m_trackElement);
     return m_trackElement->fastHasAttribute(HTMLNames::defaultAttr);
 }
 
 void LoadableTextTrack::setMode(const AtomicString& mode)
 {
     TextTrack::setMode(mode);
     if (m_trackElement->getReadyState() == HTMLTrackElement::NONE)
         m_trackElement->scheduleLoad();
 }
 
 void LoadableTextTrack::addRegions(const HeapVector<Member<VTTRegion>>& newRegions)
 {
     for (size_t i = 0; i < newRegions.size(); ++i) {
         newRegions[i]->setTrack(this);
         regions()->add(newRegions[i]);
     }
 }
 
-size_t LoadableTextTrack::trackElementIndex() const
+size_t LoadableTextTrack::trackElementIndex()
 {
-    // Count the number of preceding <track> elements (== the index.)
+    ASSERT(m_trackElement);
+    ASSERT(m_trackElement->parentNode());
+
     size_t index = 0;
-    const HTMLTrackElement* track = m_trackElement;
-    while ((track = Traversal<HTMLTrackElement>::previousSibling(*track)))
+    for (HTMLTrackElement* track = Traversal<HTMLTrackElement>::firstChild(*m_trackElement->parentNode()); track; track = Traversal<HTMLTrackElement>::nextSibling(*track)) {
+        if (!track->parentNode())
+            continue;
+        if (track == m_trackElement)
+            return index;
         ++index;
+    }
+    ASSERT_NOT_REACHED();
 
-    return index;
+    return 0;
 }
 
 DEFINE_TRACE(LoadableTextTrack)
 {
     visitor->trace(m_trackElement);
     TextTrack::trace(visitor);
 }
 
 } // namespace blink