Move getBufferedPositionUs into SequenceableLoader.

All implementations of SequenceableLoader already implement this method.
Moreover, all composite media periods contained an exact copy of an
implementation that now moved to CompositeSequencableLoader.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=162349083

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

@@ -29,7 +29,19 @@ public final class CompositeSequenceableLoader implements SequenceableLoader {
   }
 
   @Override
-  public long getNextLoadPositionUs() {
+  public final long getBufferedPositionUs() {
+    long bufferedPositionUs = Long.MAX_VALUE;
+    for (SequenceableLoader loader : loaders) {
+      long loaderBufferedPositionUs = loader.getBufferedPositionUs();
+      if (loaderBufferedPositionUs != C.TIME_END_OF_SOURCE) {
+        bufferedPositionUs = Math.min(bufferedPositionUs, loaderBufferedPositionUs);
+      }
+    }
+    return bufferedPositionUs == Long.MAX_VALUE ? C.TIME_END_OF_SOURCE : bufferedPositionUs;
+  }
+
+  @Override
+  public final long getNextLoadPositionUs() {
     long nextLoadPositionUs = Long.MAX_VALUE;
     for (SequenceableLoader loader : loaders) {
       long loaderNextLoadPositionUs = loader.getNextLoadPositionUs();
@@ -41,7 +53,7 @@ public final class CompositeSequenceableLoader implements SequenceableLoader {
   }
 
   @Override
-  public boolean continueLoading(long positionUs) {
+  public final boolean continueLoading(long positionUs) {
     boolean madeProgress = false;
     boolean madeProgressThisIteration;
     do {

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

@@ -129,16 +129,6 @@ public interface MediaPeriod extends SequenceableLoader {
   long readDiscontinuity();
 
   /**
-   * Returns an estimate of the position up to which data is buffered for the enabled tracks.
-   * <p>
-   * This method should only be called when at least one track is selected.
-   *
-   * @return An estimate of the absolute position in microseconds up to which data is buffered, or
-   *     {@link C#TIME_END_OF_SOURCE} if the track is fully buffered.
-   */
-  long getBufferedPositionUs();
-
-  /**
    * Attempts to seek to the specified position in microseconds.
    * <p>
    * After this method has been called, all {@link SampleStream}s provided by the period are
@@ -154,6 +144,17 @@ public interface MediaPeriod extends SequenceableLoader {
   // SequenceableLoader interface. Overridden to provide more specific documentation.
 
   /**
+   * Returns an estimate of the position up to which data is buffered for the enabled tracks.
+   * <p>
+   * This method should only be called when at least one track is selected.
+   *
+   * @return An estimate of the absolute position in microseconds up to which data is buffered, or
+   *     {@link C#TIME_END_OF_SOURCE} if the track is fully buffered.
+   */
+  @Override
+  long getBufferedPositionUs();
+
+  /**
    * Returns the next load time, or {@link C#TIME_END_OF_SOURCE} if loading has finished.
    * <p>
    * This method should only be called after the period has been prepared. It may be called when no

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

@@ -168,14 +168,7 @@ import java.util.IdentityHashMap;
 
   @Override
   public long getBufferedPositionUs() {
-    long bufferedPositionUs = Long.MAX_VALUE;
-    for (MediaPeriod period : enabledPeriods) {
-      long rendererBufferedPositionUs = period.getBufferedPositionUs();
-      if (rendererBufferedPositionUs != C.TIME_END_OF_SOURCE) {
-        bufferedPositionUs = Math.min(bufferedPositionUs, rendererBufferedPositionUs);
-      }
-    }
-    return bufferedPositionUs == Long.MAX_VALUE ? C.TIME_END_OF_SOURCE : bufferedPositionUs;
+    return sequenceableLoader.getBufferedPositionUs();
   }
 
   @Override

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

@@ -37,6 +37,14 @@ public interface SequenceableLoader {
   }
 
   /**
+   * Returns an estimate of the position up to which data is buffered.
+   *
+   * @return An estimate of the absolute position in microseconds up to which data is buffered, or
+   *     {@link C#TIME_END_OF_SOURCE} if the data is fully buffered.
+   */
+  long getBufferedPositionUs();
+
+  /**
    * Returns the next load time, or {@link C#TIME_END_OF_SOURCE} if loading has finished.
    */
   long getNextLoadPositionUs();

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

@@ -209,14 +209,7 @@ import java.util.List;
 
   @Override
   public long getBufferedPositionUs() {
-    long bufferedPositionUs = Long.MAX_VALUE;
-    for (ChunkSampleStream<DashChunkSource> sampleStream : sampleStreams) {
-      long rendererBufferedPositionUs = sampleStream.getBufferedPositionUs();
-      if (rendererBufferedPositionUs != C.TIME_END_OF_SOURCE) {
-        bufferedPositionUs = Math.min(bufferedPositionUs, rendererBufferedPositionUs);
-      }
-    }
-    return bufferedPositionUs == Long.MAX_VALUE ? C.TIME_END_OF_SOURCE : bufferedPositionUs;
+    return sequenceableLoader.getBufferedPositionUs();
   }
 
   @Override

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

@@ -203,14 +203,7 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
 
   @Override
   public long getBufferedPositionUs() {
-    long bufferedPositionUs = Long.MAX_VALUE;
-    for (HlsSampleStreamWrapper sampleStreamWrapper : enabledSampleStreamWrappers) {
-      long rendererBufferedPositionUs = sampleStreamWrapper.getBufferedPositionUs();
-      if (rendererBufferedPositionUs != C.TIME_END_OF_SOURCE) {
-        bufferedPositionUs = Math.min(bufferedPositionUs, rendererBufferedPositionUs);
-      }
-    }
-    return bufferedPositionUs == Long.MAX_VALUE ? C.TIME_END_OF_SOURCE : bufferedPositionUs;
+    return sequenceableLoader.getBufferedPositionUs();
   }
 
   @Override

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

@@ -159,14 +159,7 @@ import java.util.ArrayList;
 
   @Override
   public long getBufferedPositionUs() {
-    long bufferedPositionUs = Long.MAX_VALUE;
-    for (ChunkSampleStream<SsChunkSource> sampleStream : sampleStreams) {
-      long rendererBufferedPositionUs = sampleStream.getBufferedPositionUs();
-      if (rendererBufferedPositionUs != C.TIME_END_OF_SOURCE) {
-        bufferedPositionUs = Math.min(bufferedPositionUs, rendererBufferedPositionUs);
-      }
-    }
-    return bufferedPositionUs == Long.MAX_VALUE ? C.TIME_END_OF_SOURCE : bufferedPositionUs;
+    return sequenceableLoader.getBufferedPositionUs();
   }
 
   @Override