Propagate playlist loading error if it prevents playback

This imitates DashMediaSource's behavior.

Issue:#2623

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=155485738

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

@@ -92,6 +92,7 @@ public void clear() {
   private boolean isTimestampMaster;
   private byte[] scratchSpace;
   private IOException fatalError;
+  private HlsUrl expectedPlaylistUrl;
 
   private Uri encryptionKeyUri;
   private byte[] encryptionKey;
@@ -143,6 +144,9 @@ public void maybeThrowError() throws IOException {
     if (fatalError != null) {
       throw fatalError;
     }
+    if (expectedPlaylistUrl != null) {
+      playlistTracker.maybeThrowPlaylistRefreshError(expectedPlaylistUrl);
+    }
   }
 
   /**
@@ -195,6 +199,7 @@ public void setIsTimestampMaster(boolean isTimestampMaster) {
   public void getNextChunk(HlsMediaChunk previous, long playbackPositionUs, HlsChunkHolder out) {
     int oldVariantIndex = previous == null ? C.INDEX_UNSET
         : trackGroup.indexOf(previous.trackFormat);
+    expectedPlaylistUrl = null;
     // Use start time of the previous chunk rather than its end time because switching format will
     // require downloading overlapping segments.
     long bufferedDurationUs = previous == null ? 0
@@ -208,6 +213,7 @@ public void getNextChunk(HlsMediaChunk previous, long playbackPositionUs, HlsChu
     HlsUrl selectedUrl = variants[selectedVariantIndex];
     if (!playlistTracker.isSnapshotValid(selectedUrl)) {
       out.playlist = selectedUrl;
+      expectedPlaylistUrl = selectedUrl;
       // Retry when playlist is refreshed.
       return;
     }
@@ -247,6 +253,7 @@ public void getNextChunk(HlsMediaChunk previous, long playbackPositionUs, HlsChu
         out.endOfStream = true;
       } else /* Live */ {
         out.playlist = selectedUrl;
+        expectedPlaylistUrl = selectedUrl;
       }
       return;
     }

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

@@ -84,7 +84,7 @@ public void prepareSource(ExoPlayer player, boolean isTopLevelSource, Listener l
 
   @Override
   public void maybeThrowSourceInfoRefreshError() throws IOException {
-    playlistTracker.maybeThrowPlaylistRefreshError();
+    playlistTracker.maybeThrowPrimaryPlaylistRefreshError();
   }
 
   @Override

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

@@ -200,18 +200,29 @@ public void release() {
   }
 
   /**
-   * If the tracker is having trouble refreshing the primary playlist or loading an irreplaceable
-   * playlist, this method throws the underlying error. Otherwise, does nothing.
+   * If the tracker is having trouble refreshing the master playlist or the primary playlist, this
+   * method throws the underlying error. Otherwise, does nothing.
    *
    * @throws IOException The underlying error.
    */
-  public void maybeThrowPlaylistRefreshError() throws IOException {
+  public void maybeThrowPrimaryPlaylistRefreshError() throws IOException {
     initialPlaylistLoader.maybeThrowError();
     if (primaryHlsUrl != null) {
-      playlistBundles.get(primaryHlsUrl).mediaPlaylistLoader.maybeThrowError();
+      maybeThrowPlaylistRefreshError(primaryHlsUrl);
     }
   }
 
+  /**
+   * If the playlist is having trouble loading the playlist referenced by the given {@link HlsUrl},
+   * this method throws the underlying error.
+   *
+   * @param url The {@link HlsUrl}.
+   * @throws IOException The underyling error.
+   */
+  public void maybeThrowPlaylistRefreshError(HlsUrl url) throws IOException {
+    playlistBundles.get(url).mediaPlaylistLoader.maybeThrowError();
+  }
+
   /**
    * Triggers a playlist refresh and whitelists it.
    *