feat(MediaSource): client code can get the tag of a MediaSource

extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsMediaSource.java

@@ -76,6 +76,12 @@ public ImaAdsMediaSource(
         adUiViewGroup, eventHandler, eventListener);
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return adsMediaSource.getTag();
+  }
+
   @Override
   public void prepareSourceInternal(
       final ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/ClippingMediaSource.java

@@ -186,6 +186,12 @@ public ClippingMediaSource(
     window = new Timeline.Window();
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return mediaSource.getTag();
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java

@@ -453,6 +453,12 @@ public final synchronized void setShuffleOrder(
     }
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return null;
+  }
+
   @Override
   public final synchronized void prepareSourceInternal(
       ExoPlayer player,
@@ -1069,6 +1075,12 @@ protected void prepareSourceInternal(
       // Do nothing.
     }
 
+    @Override
+    @Nullable
+    public Object getTag() {
+      return null;
+    }
+
     @Override
     protected void releaseSourceInternal() {
       // Do nothing.

library/core/src/main/java/com/google/android/exoplayer2/source/ExtractorMediaSource.java

@@ -358,6 +358,12 @@ private ExtractorMediaSource(
     this.tag = tag;
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return tag;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/LoopingMediaSource.java

@@ -64,6 +64,12 @@ public LoopingMediaSource(MediaSource childSource, int loopCount) {
     mediaPeriodToChildMediaPeriodId = new HashMap<>();
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return childSource.getTag();
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/MediaSource.java

@@ -219,6 +219,13 @@ public int hashCode() {
    */
   void removeEventListener(MediaSourceEventListener eventListener);
 
+  /**
+   * Returns the tag set on the media source, or null when none was set.
+   */
+  @Nullable default Object getTag() {
+    return null;
+  }
+
   /**
    * Starts source preparation if not yet started, and adds a listener for timeline and/or manifest
    * updates.

library/core/src/main/java/com/google/android/exoplayer2/source/MergingMediaSource.java

@@ -98,6 +98,12 @@ public MergingMediaSource(CompositeSequenceableLoaderFactory compositeSequenceab
     timelines = new Timeline[mediaSources.length];
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return mediaSources.length > 0 ? mediaSources[0].getTag() : null;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/SingleSampleMediaSource.java

@@ -185,6 +185,7 @@ public SingleSampleMediaSource createMediaSource(
   private final LoadErrorHandlingPolicy loadErrorHandlingPolicy;
   private final boolean treatLoadErrorsAsEndOfStream;
   private final Timeline timeline;
+  private final @Nullable Object tag;
 
   private @Nullable TransferListener transferListener;
 
@@ -287,6 +288,7 @@ private SingleSampleMediaSource(
     this.durationUs = durationUs;
     this.loadErrorHandlingPolicy = loadErrorHandlingPolicy;
     this.treatLoadErrorsAsEndOfStream = treatLoadErrorsAsEndOfStream;
+    this.tag = tag;
     dataSpec =
         new DataSpec(uri, DataSpec.FLAG_ALLOW_GZIP | DataSpec.FLAG_ALLOW_CACHING_UNKNOWN_LENGTH);
     timeline =
@@ -295,6 +297,12 @@ private SingleSampleMediaSource(
 
   // MediaSource implementation.
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return tag;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/core/src/main/java/com/google/android/exoplayer2/source/ads/AdsMediaSource.java

@@ -319,6 +319,12 @@ public AdsMediaSource(
     adsLoader.setSupportedContentTypes(adMediaSourceFactory.getSupportedTypes());
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return contentMediaSource.getTag();
+  }
+
   @Override
   public void prepareSourceInternal(
       final ExoPlayer player,

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java

@@ -607,6 +607,12 @@ public void replaceManifestUri(Uri manifestUri) {
 
   // MediaSource implementation.
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return tag;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

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

@@ -390,6 +390,12 @@ private HlsMediaSource(
     this.tag = tag;
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return tag;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

library/smoothstreaming/src/main/java/com/google/android/exoplayer2/source/smoothstreaming/SsMediaSource.java

@@ -503,6 +503,12 @@ private SsMediaSource(
 
   // MediaSource implementation.
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    return tag;
+  }
+
   @Override
   public void prepareSourceInternal(
       ExoPlayer player,

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeMediaSource.java

@@ -88,6 +88,14 @@ public FakeMediaSource(@Nullable Timeline timeline, Object manifest,
     this.trackGroupArray = trackGroupArray;
   }
 
+  @Override
+  @Nullable
+  public Object getTag() {
+    boolean hasTimeline = timeline != null && !timeline.isEmpty();
+
+    return hasTimeline ? timeline.getWindow(0, new Timeline.Window()).tag : null;
+  }
+
   @Override
   public synchronized void prepareSourceInternal(
       ExoPlayer player,