Simplify LoadableTextTrack::trackElementIndex

third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp

Index: third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp
diff --git a/third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp b/third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp
index c61c4fd9a6b425d5b5dad9a559e28296d4db28e3..98aafb77d566ddd548e000794381b109d381336d 100644
--- a/third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp
+++ b/third_party/WebKit/Source/core/html/track/LoadableTextTrack.cpp
@@ -35,6 +35,7 @@ LoadableTextTrack::LoadableTextTrack(HTMLTrackElement* track)
     : TextTrack(subtitlesKeyword(), emptyAtom, emptyAtom, emptyAtom, TrackElement)
     , m_trackElement(track)
 {
+    DCHECK(m_trackElement);
 }
 
 LoadableTextTrack::~LoadableTextTrack()
@@ -43,7 +44,6 @@ LoadableTextTrack::~LoadableTextTrack()
 
 bool LoadableTextTrack::isDefault() const
 {
-    ASSERT(m_trackElement);
     return m_trackElement->fastHasAttribute(HTMLNames::defaultAttr);
 }
 
@@ -62,22 +62,16 @@ void LoadableTextTrack::addRegions(const HeapVector<Member<VTTRegion>>& newRegio
     }
 }
 
-size_t LoadableTextTrack::trackElementIndex()
+size_t LoadableTextTrack::trackElementIndex() const
 {
-    ASSERT(m_trackElement);
-    ASSERT(m_trackElement->parentNode());
-
+    // Count the number of preceding <track> elements (== the index.)
     size_t index = 0;
-    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;
+    for (const HTMLTrackElement* track = Traversal<HTMLTrackElement>::previousSibling(*m_trackElement);
+        track;
+        track = Traversal<HTMLTrackElement>::previousSibling(*track))
         ++index;
-    }
-    ASSERT_NOT_REACHED();
 
-    return 0;
+    return index;
 }
 
 DEFINE_TRACE(LoadableTextTrack)