Add support for AC-3 streams in HLS

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131398594

demo/src/main/assets/sample_media.exolist.json

@@ -296,14 +296,18 @@
     "name": "HLS",
     "samples": [
       {
-        "name": "Apple master playlist",
+        "name": "Apple 4x3 basic stream",
         "uri": "https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_4x3/bipbop_4x3_variant.m3u8"
       },
       {
-        "name": "Apple master playlist advanced",
+        "name": "Apple 16x9 basic stream",
         "uri": "https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_16x9/bipbop_16x9_variant.m3u8"
       },
       {
+        "name": "Apple master playlist advanced",
+        "uri": "https://tungsten.aaplimg.com/VOD/bipbop_adv_example_v2/master.m3u8"
+      },
+      {
         "name": "Apple TS media playlist",
         "uri": "https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_4x3/gear1/prog_index.m3u8"
       },

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

@@ -22,6 +22,7 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.extractor.Extractor;
 import com.google.android.exoplayer2.extractor.mp3.Mp3Extractor;
+import com.google.android.exoplayer2.extractor.ts.Ac3Extractor;
 import com.google.android.exoplayer2.extractor.ts.AdtsExtractor;
 import com.google.android.exoplayer2.extractor.ts.PtsTimestampAdjuster;
 import com.google.android.exoplayer2.extractor.ts.TsExtractor;
@@ -63,6 +64,7 @@ public class HlsChunkSource {
   private static final double LIVE_VARIANT_SWITCH_SAFETY_EXTRA_SECS = 2.0;
   private static final String TAG = "HlsChunkSource";
   private static final String AAC_FILE_EXTENSION = ".aac";
+  private static final String AC3_FILE_EXTENSION = ".ac3";
   private static final String MP3_FILE_EXTENSION = ".mp3";
   private static final String VTT_FILE_EXTENSION = ".vtt";
   private static final String WEBVTT_FILE_EXTENSION = ".webvtt";
@@ -286,6 +288,8 @@ public class HlsChunkSource {
       // identifier com.apple.streaming.transportStreamTimestamp. This may also apply to the MP3
       // case below.
       extractor = new AdtsExtractor(startTimeUs);
+    } else if (lastPathSegment.endsWith(AC3_FILE_EXTENSION)) {
+      extractor = new Ac3Extractor(startTimeUs);
     } else if (lastPathSegment.endsWith(MP3_FILE_EXTENSION)) {
       extractor = new Mp3Extractor(startTimeUs);
     } else if (lastPathSegment.endsWith(WEBVTT_FILE_EXTENSION)