Use StreamParser::TrackId instead of string for MediaTrack::byteStreamTrackId

media/formats/webm/webm_tracks_parser.cc

Index: media/formats/webm/webm_tracks_parser.cc
diff --git a/media/formats/webm/webm_tracks_parser.cc b/media/formats/webm/webm_tracks_parser.cc
index f518c721dfb4704f7d028c2e1f74d28aef0c22ea..bcd33e487f3a9a57ce5af8511b5ba7f4eaffac3d 100644
--- a/media/formats/webm/webm_tracks_parser.cc
+++ b/media/formats/webm/webm_tracks_parser.cc
@@ -221,9 +221,10 @@ bool WebMTracksParser::OnListEnd(int id) {
                 encryption_scheme, &audio_decoder_config_)) {
           return false;
         }
-        media_tracks_->AddAudioTrack(audio_decoder_config_,
-                                     base::Uint64ToString(track_num_), "main",
-                                     track_name_, track_language_);
+        media_tracks_->AddAudioTrack(
+            audio_decoder_config_,
+            static_cast<StreamParser::TrackId>(track_num_), "main", track_name_,
+            track_language_);
       } else {
         MEDIA_LOG(DEBUG, media_log_) << "Ignoring audio track " << track_num_;
         ignored_tracks_.insert(track_num_);
@@ -247,9 +248,10 @@ bool WebMTracksParser::OnListEnd(int id) {
                                             &video_decoder_config_)) {
           return false;
         }
-        media_tracks_->AddVideoTrack(video_decoder_config_,
-                                     base::Uint64ToString(track_num_), "main",
-                                     track_name_, track_language_);
+        media_tracks_->AddVideoTrack(
+            video_decoder_config_,
+            static_cast<StreamParser::TrackId>(track_num_), "main", track_name_,
+            track_language_);
       } else {
         MEDIA_LOG(DEBUG, media_log_) << "Ignoring video track " << track_num_;
         ignored_tracks_.insert(track_num_);