Add support for reading .mp3 boxes in stsd.

This is used by Quicktime for MP3 tracks.

Issue: #2066

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139209989

library/src/main/java/com/google/android/exoplayer2/extractor/mp4/Atom.java

@@ -52,6 +52,7 @@ import java.util.List;
   public static final int TYPE_d263 = Util.getIntegerCodeForString("d263");
   public static final int TYPE_mdat = Util.getIntegerCodeForString("mdat");
   public static final int TYPE_mp4a = Util.getIntegerCodeForString("mp4a");
+  public static final int TYPE__mp3 = Util.getIntegerCodeForString(".mp3");
   public static final int TYPE_wave = Util.getIntegerCodeForString("wave");
   public static final int TYPE_lpcm = Util.getIntegerCodeForString("lpcm");
   public static final int TYPE_sowt = Util.getIntegerCodeForString("sowt");

library/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java

@@ -600,7 +600,8 @@ import java.util.List;
           || childAtomType == Atom.TYPE_dtsc || childAtomType == Atom.TYPE_dtse
           || childAtomType == Atom.TYPE_dtsh || childAtomType == Atom.TYPE_dtsl
           || childAtomType == Atom.TYPE_samr || childAtomType == Atom.TYPE_sawb
-          || childAtomType == Atom.TYPE_lpcm || childAtomType == Atom.TYPE_sowt) {
+          || childAtomType == Atom.TYPE_lpcm || childAtomType == Atom.TYPE_sowt
+          || childAtomType == Atom.TYPE__mp3) {
         parseAudioSampleEntry(stsd, childAtomType, childStartPosition, childAtomSize, trackId,
             language, isQuickTime, drmInitData, out, i);
       } else if (childAtomType == Atom.TYPE_TTML) {
@@ -829,6 +830,8 @@ import java.util.List;
       mimeType = MimeTypes.AUDIO_AMR_WB;
     } else if (atomType == Atom.TYPE_lpcm || atomType == Atom.TYPE_sowt) {
       mimeType = MimeTypes.AUDIO_RAW;
+    } else if (atomType == Atom.TYPE__mp3) {
+      mimeType = MimeTypes.AUDIO_MPEG;
     }
 
     byte[] initializationData = null;