Add URLs EXT-X-STREAM-INF uris only once

This prevents ExoPlayer from thinking there are many more video tracks
than there actually are. And will prevent downloading multiple times
the same rendition once offline support for HLS is added.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=160285777

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/playlist/HlsPlaylistParser.java

@@ -30,6 +30,7 @@ import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.InputStreamReader;
 import java.util.ArrayList;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.List;
 import java.util.Queue;
 import java.util.Queue;
@@ -174,6 +175,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
 
 
   private static HlsMasterPlaylist parseMasterPlaylist(LineIterator iterator, String baseUri)
   private static HlsMasterPlaylist parseMasterPlaylist(LineIterator iterator, String baseUri)
       throws IOException {
       throws IOException {
+    HashSet<String> variantUrls = new HashSet<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> variants = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> variants = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> audios = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> audios = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> subtitles = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> subtitles = new ArrayList<>();
@@ -251,13 +253,15 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
           width = Format.NO_VALUE;
           width = Format.NO_VALUE;
           height = Format.NO_VALUE;
           height = Format.NO_VALUE;
         }
         }
-        line = iterator.next();
+        line = iterator.next(); // #EXT-X-STREAM-INF's URI.
+        if (variantUrls.add(line)) {
           Format format = Format.createVideoContainerFormat(Integer.toString(variants.size()),
           Format format = Format.createVideoContainerFormat(Integer.toString(variants.size()),
-            MimeTypes.APPLICATION_M3U8, null, codecs, bitrate, width, height, Format.NO_VALUE, null,
-            0);
+              MimeTypes.APPLICATION_M3U8, null, codecs, bitrate, width, height, Format.NO_VALUE,
+              null, 0);
           variants.add(new HlsMasterPlaylist.HlsUrl(line, format));
           variants.add(new HlsMasterPlaylist.HlsUrl(line, format));
         }
         }
       }
       }
+    }
     if (noClosedCaptions) {
     if (noClosedCaptions) {
       muxedCaptionFormats = Collections.emptyList();
       muxedCaptionFormats = Collections.emptyList();
     }
     }