Implement VTTCue.region and sync the VTTRegion interface

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 37 matching lines @@
 }
 
 void LoadableTextTrack::setMode(const AtomicString& mode) {
   TextTrack::setMode(mode);
   if (m_trackElement->getReadyState() == HTMLTrackElement::kNone)
     m_trackElement->scheduleLoad();
 }
 
 void LoadableTextTrack::addRegions(
     const HeapVector<Member<VTTRegion>>& newRegions) {
-  for (const auto& region : newRegions) {
-    region->setTrack(this);
+  for (const auto& region : newRegions)
     regions()->add(region);
-  }
 }
 
 size_t LoadableTextTrack::trackElementIndex() const {
   // Count the number of preceding <track> elements (== the index.)
   size_t index = 0;
   for (const HTMLTrackElement* track =
            Traversal<HTMLTrackElement>::previousSibling(*m_trackElement);
        track; track = Traversal<HTMLTrackElement>::previousSibling(*track))
     ++index;
 
   return index;
 }
 
 DEFINE_TRACE(LoadableTextTrack) {
   visitor->trace(m_trackElement);
   TextTrack::trace(visitor);
 }
 
 }  // namespace blink