Fix handling of self initializing segments in DASH

The parsing of multiple moov boxes for a single ExtractorOutput incurred in
an assertion failure due to repeated track declarations. This CL makes each
new moov box replace any previous one. This change is transparent to the
client, no flags are provided to allow this feature.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117236246

library/src/main/java/com/google/android/exoplayer/extractor/mp4/FragmentedMp4Extractor.java

@@ -143,6 +143,7 @@ public final class FragmentedMp4Extractor implements Extractor {
     extendedTypeScratch = new byte[16];
     containerAtoms = new Stack<>();
     trackBundles = new SparseArray<>();
+    durationUs = C.UNKNOWN_TIME_US;
     enterReadingAtomHeaderState();
   }
 
@@ -155,8 +156,9 @@ public final class FragmentedMp4Extractor implements Extractor {
   public void init(ExtractorOutput output) {
     extractorOutput = output;
     if (sideloadedTrack != null) {
-      trackBundles.put(0, new TrackBundle(sideloadedTrack, new TrackFragment(), output.track(0),
-          new DefaultSampleValues(0, 0, 0, 0)));
+      TrackBundle bundle = new TrackBundle(output.track(0));
+      bundle.init(sideloadedTrack, new DefaultSampleValues(0, 0, 0, 0));
+      trackBundles.put(0, bundle);
       extractorOutput.endTracks();
     }
   }
@@ -324,7 +326,7 @@ public final class FragmentedMp4Extractor implements Extractor {
       extractorOutput.drmInitData(drmInitData);
     }
 
-    // Read declaration of Track Fragments in the Moov box.
+    // Read declaration of track fragments in the Moov box.
     ContainerAtom mvex = moov.getContainerAtomOfType(Atom.TYPE_mvex);
     SparseArray<DefaultSampleValues> defaultSampleValuesArray = new SparseArray<>();
     int mvexChildrenSize = mvex.leafChildren.size();
@@ -336,26 +338,37 @@ public final class FragmentedMp4Extractor implements Extractor {
       }
     }
 
-    // Construction of Tracks and TrackOutputs.
-    durationUs = C.UNKNOWN_TIME_US;
-    trackBundles.clear();
+    // Construction of tracks.
+    SparseArray<Track> tracks = new SparseArray<>();
     int moovContainerChildrenSize = moov.containerChildren.size();
-    int trackBundlesSize = 0;
     for (int i = 0; i < moovContainerChildrenSize; i++) {
       Atom.ContainerAtom atom = moov.containerChildren.get(i);
       if (atom.type == Atom.TYPE_trak) {
         Track track = AtomParsers.parseTrak(atom, moov.getLeafAtomOfType(Atom.TYPE_mvhd), false);
         if (track != null) {
-          DefaultSampleValues defaultSampleValues = defaultSampleValuesArray.get(track.id);
-          TrackBundle bundle = new TrackBundle(track, new TrackFragment(),
-              extractorOutput.track(trackBundlesSize++), defaultSampleValues);
-          bundle.output.format(track.format);
-          trackBundles.put(track.id, bundle);
-          durationUs = Math.max(track.durationUs, durationUs);
+          tracks.put(track.id, track);
         }
       }
     }
-    extractorOutput.endTracks();
+
+    int trackCount = tracks.size();
+    if (trackBundles.size() == 0) {
+      // We need to create the track bundles.
+      for (int i = 0; i < trackCount; i++) {
+        Track track = tracks.valueAt(i);
+        trackBundles.put(track.id, new TrackBundle(extractorOutput.track(i)));
+        durationUs = Math.max(durationUs, track.durationUs);
+      }
+      extractorOutput.endTracks();
+    } else {
+      Assertions.checkState(trackBundles.size() == trackCount);
+    }
+
+    // Initialization of tracks and default sample values.
+    for (int i = 0; i < trackCount; i++) {
+      Track track = tracks.valueAt(i);
+      trackBundles.get(track.id).init(track, defaultSampleValuesArray.get(track.id));
+    }
   }
 
   private void onMoofContainerAtomRead(ContainerAtom moof) throws ParserException {
@@ -951,18 +964,24 @@ public final class FragmentedMp4Extractor implements Extractor {
    */
   private static final class TrackBundle {
 
-    public final Track track;
     public final TrackFragment fragment;
     public final TrackOutput output;
-    public final DefaultSampleValues defaultSampleValues;
+
+    public Track track;
+    public DefaultSampleValues defaultSampleValues;
     public int currentSampleIndex;
 
-    public TrackBundle(Track track, TrackFragment fragment, TrackOutput output,
-        DefaultSampleValues defaultSampleValues) {
+    public TrackBundle(TrackOutput output) {
+      fragment = new TrackFragment();
+      this.output = output;
+    }
+
+    public void init(Track track, DefaultSampleValues defaultSampleValues) {
       this.track = Assertions.checkNotNull(track);
-      this.fragment = Assertions.checkNotNull(fragment);
-      this.output = Assertions.checkNotNull(output);
       this.defaultSampleValues = Assertions.checkNotNull(defaultSampleValues);
+      output.format(track.format);
+      fragment.reset();
+      currentSampleIndex = 0;
     }
 
   }