Use new downcast helper for blink::LoadableTextTrack

This CL has two goals,
  1. Use To<LoadableTextTrack> and DynamicTo<LoadableTextTrack> as new
     downcast helper
  2. Use IsA<LoadableTextTrack>(element) in place of
     IsLoadableTextTrack(element)

Bug: 891908
Change-Id: I1b96f72a9904c8a64813f14d085f42e16c2e8628
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2018352Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Abhijeet Kandalkar <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#746234}

third_party/blink/renderer/core/html/media/html_media_element.cc

@@ -81,6 +81,7 @@
 #include "third_party/blink/renderer/core/html/track/cue_timeline.h"
 #include "third_party/blink/renderer/core/html/track/html_track_element.h"
 #include "third_party/blink/renderer/core/html/track/inband_text_track.h"
+#include "third_party/blink/renderer/core/html/track/loadable_text_track.h"
 #include "third_party/blink/renderer/core/html/track/text_track_container.h"
 #include "third_party/blink/renderer/core/html/track/text_track_list.h"
 #include "third_party/blink/renderer/core/html/track/video_track.h"
@@ -1459,7 +1460,7 @@ void HTMLMediaElement::TextTrackReadyStateChanged(TextTrack* track) {
 void HTMLMediaElement::TextTrackModeChanged(TextTrack* track) {
   // Mark this track as "configured" so configureTextTracks won't change the
   // mode again.
-  if (track->TrackType() == TextTrack::kTrackElement)
+  if (IsA<LoadableTextTrack>(track))
     track->SetHasBeenConfigured(true);
 
   if (track->IsRendered()) {

third_party/blink/renderer/core/html/track/cue_timeline.cc

@@ -324,9 +324,8 @@ void CueTimeline::UpdateActiveCues(double movie_time) {
 
     // ... if the text track has a corresponding track element, to then fire a
     // simple event named cuechange at the track element as well.
-    if (track->TrackType() == TextTrack::kTrackElement) {
-      HTMLTrackElement* track_element =
-          ToLoadableTextTrack(track.Get())->TrackElement();
+    if (auto* loadable_text_track = DynamicTo<LoadableTextTrack>(track.Get())) {
+      HTMLTrackElement* track_element = loadable_text_track->TrackElement();
       DCHECK(track_element);
       media_element.ScheduleEvent(
           CreateEventWithTarget(event_type_names::kCuechange, track_element));

third_party/blink/renderer/core/html/track/loadable_text_track.h

@@ -55,11 +55,12 @@ class LoadableTextTrack final : public TextTrack {
   Member<HTMLTrackElement> track_element_;
 };
 
-DEFINE_TYPE_CASTS(LoadableTextTrack,
-                  TextTrack,
-                  track,
-                  track->TrackType() == TextTrack::kTrackElement,
-                  track.TrackType() == TextTrack::kTrackElement);
+template <>
+struct DowncastTraits<LoadableTextTrack> {
+  static bool AllowFrom(const TextTrack& track) {
+    return track.TrackType() == TextTrack::kTrackElement;
+  }
+};
 
 }  // namespace blink
 

third_party/blink/renderer/core/html/track/text_track_list.cc

@@ -44,8 +44,8 @@ unsigned TextTrackList::length() const {
 }
 
 int TextTrackList::GetTrackIndex(TextTrack* text_track) {
-  if (text_track->TrackType() == TextTrack::kTrackElement)
-    return ToLoadableTextTrack(text_track)->TrackElementIndex();
+  if (auto* loadable_text_track = DynamicTo<LoadableTextTrack>(text_track))
+    return loadable_text_track->TrackElementIndex();
 
   if (text_track->TrackType() == TextTrack::kAddTrack)
     return element_tracks_.size() + add_track_tracks_.Find(text_track);
@@ -141,7 +141,7 @@ TextTrack* TextTrackList::getTrackById(const AtomicString& id) {
 void TextTrackList::InvalidateTrackIndexesAfterTrack(TextTrack* track) {
   HeapVector<Member<TextTrack>>* tracks = nullptr;
 
-  if (track->TrackType() == TextTrack::kTrackElement) {
+  if (IsA<LoadableTextTrack>(track)) {
     tracks = &element_tracks_;
     for (const auto& add_track : add_track_tracks_)
       add_track->InvalidateTrackIndex();
@@ -168,9 +168,9 @@ void TextTrackList::InvalidateTrackIndexesAfterTrack(TextTrack* track) {
 void TextTrackList::Append(TextTrack* track) {
   if (track->TrackType() == TextTrack::kAddTrack) {
     add_track_tracks_.push_back(track);
-  } else if (track->TrackType() == TextTrack::kTrackElement) {
+  } else if (auto* loadable_text_track = DynamicTo<LoadableTextTrack>(track)) {
     // Insert tracks added for <track> element in tree order.
-    wtf_size_t index = ToLoadableTextTrack(track)->TrackElementIndex();
+    wtf_size_t index = loadable_text_track->TrackElementIndex();
     element_tracks_.insert(index, track);
   } else if (track->TrackType() == TextTrack::kInBand) {
     inband_tracks_.push_back(track);
@@ -189,7 +189,7 @@ void TextTrackList::Append(TextTrack* track) {
 void TextTrackList::Remove(TextTrack* track) {
   HeapVector<Member<TextTrack>>* tracks = nullptr;
 
-  if (track->TrackType() == TextTrack::kTrackElement) {
+  if (IsA<LoadableTextTrack>(track)) {
     tracks = &element_tracks_;
   } else if (track->TrackType() == TextTrack::kAddTrack) {
     tracks = &add_track_tracks_;
@@ -223,7 +223,7 @@ void TextTrackList::RemoveAllInbandTracks() {
 bool TextTrackList::Contains(TextTrack* track) const {
   const HeapVector<Member<TextTrack>>* tracks = nullptr;
 
-  if (track->TrackType() == TextTrack::kTrackElement)
+  if (IsA<LoadableTextTrack>(track))
     tracks = &element_tracks_;
   else if (track->TrackType() == TextTrack::kAddTrack)
     tracks = &add_track_tracks_;