Add HlsMasterPlaylist.copy method

Creates a copy of this playlist which includes only the variants identified by the given variantUrls.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=163212562

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

@@ -17,6 +17,7 @@ package com.google.android.exoplayer2.source.hls.playlist;
 
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.util.MimeTypes;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
@@ -108,6 +109,20 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
         ? Collections.unmodifiableList(muxedCaptionFormats) : null;
   }
 
+  /**
+   * Returns a copy of this playlist which includes only the renditions identified by the given
+   * urls.
+   *
+   * @param renditionUrls List of rendition urls.
+   * @return A copy of this playlist which includes only the renditions identified by the given
+   *     urls.
+   */
+  public HlsMasterPlaylist copy(List<String> renditionUrls) {
+    return new HlsMasterPlaylist(baseUri, tags, copyRenditionList(variants, renditionUrls),
+        copyRenditionList(audios, renditionUrls), copyRenditionList(subtitles, renditionUrls),
+        muxedAudioFormat, muxedCaptionFormats);
+  }
+
   /**
    * Creates a playlist with a single variant.
    *
@@ -121,4 +136,15 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
         emptyList, null, null);
   }
 
+  private static List<HlsUrl> copyRenditionList(List<HlsUrl> variants, List<String> variantUrls) {
+    List<HlsUrl> copyVariants = new ArrayList<>();
+    for (int i = 0; i < variants.size(); i++) {
+      HlsUrl variant = variants.get(i);
+      if (variantUrls.contains(variant.url)) {
+        copyVariants.add(variant);
+      }
+    }
+    return copyVariants;
+  }
+
 }