Check the type of the (non-initial) loaded HLS playlist

This prevents illegal casts.

Issue:#2702

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154078240

library/hls/src/androidTest/java/com/google/android/exoplayer2/source/hls/playlist/HlsMediaPlaylistParserTest.java

@@ -70,7 +70,6 @@ public class HlsMediaPlaylistParserTest extends TestCase {
     try {
       HlsPlaylist playlist = new HlsPlaylistParser().parse(playlistUri, inputStream);
       assertNotNull(playlist);
-      assertEquals(HlsPlaylist.TYPE_MEDIA, playlist.type);
 
       HlsMediaPlaylist mediaPlaylist = (HlsMediaPlaylist) playlist;
       assertEquals(HlsMediaPlaylist.PLAYLIST_TYPE_VOD, mediaPlaylist.playlistType);

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

@@ -55,7 +55,7 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
 
   public HlsMasterPlaylist(String baseUri, List<HlsUrl> variants, List<HlsUrl> audios,
       List<HlsUrl> subtitles, Format muxedAudioFormat, List<Format> muxedCaptionFormats) {
-    super(baseUri, HlsPlaylist.TYPE_MASTER);
+    super(baseUri);
     this.variants = Collections.unmodifiableList(variants);
     this.audios = Collections.unmodifiableList(audios);
     this.subtitles = Collections.unmodifiableList(subtitles);

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

@@ -97,7 +97,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
       long startTimeUs, boolean hasDiscontinuitySequence, int discontinuitySequence,
       int mediaSequence, int version, long targetDurationUs, boolean hasEndTag,
       boolean hasProgramDateTime, Segment initializationSegment, List<Segment> segments) {
-    super(baseUri, HlsPlaylist.TYPE_MEDIA);
+    super(baseUri);
     this.playlistType = playlistType;
     this.startTimeUs = startTimeUs;
     this.hasDiscontinuitySequence = hasDiscontinuitySequence;

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

@@ -15,30 +15,15 @@
  */
 package com.google.android.exoplayer2.source.hls.playlist;
 
-import android.support.annotation.IntDef;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
-
 /**
  * Represents an HLS playlist.
  */
 public abstract class HlsPlaylist {
 
-  /**
-   * The type of playlist.
-   */
-  @Retention(RetentionPolicy.SOURCE)
-  @IntDef({TYPE_MASTER, TYPE_MEDIA})
-  public @interface Type {}
-  public static final int TYPE_MASTER = 0;
-  public static final int TYPE_MEDIA = 1;
-
   public final String baseUri;
-  @Type public final int type;
 
-  protected HlsPlaylist(String baseUri, @Type int type) {
+  protected HlsPlaylist(String baseUri) {
     this.baseUri = baseUri;
-    this.type = type;
   }
 
 }

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

@@ -477,9 +477,15 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
     @Override
     public void onLoadCompleted(ParsingLoadable<HlsPlaylist> loadable, long elapsedRealtimeMs,
         long loadDurationMs) {
-      processLoadedPlaylist((HlsMediaPlaylist) loadable.getResult());
+      HlsPlaylist result = loadable.getResult();
+      if (result instanceof HlsMediaPlaylist) {
+        processLoadedPlaylist((HlsMediaPlaylist) result);
         eventDispatcher.loadCompleted(loadable.dataSpec, C.DATA_TYPE_MANIFEST, elapsedRealtimeMs,
             loadDurationMs, loadable.bytesLoaded());
+      } else {
+        onLoadError(loadable, elapsedRealtimeMs, loadDurationMs,
+            new ParserException("Loaded playlist has unexpected type."));
+      }
     }
 
     @Override