Fix discarding upstream from DefaultTrackOutput

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=158837777

library/core/src/androidTest/java/com/google/android/exoplayer2/extractor/DefaultTrackOutputTest.java

@@ -251,6 +251,68 @@ public class DefaultTrackOutputTest extends TestCase {
     assertNoSamplesToRead(TEST_FORMAT_2);
     assertNoSamplesToRead(TEST_FORMAT_2);
   }
   }
 
 
+  public void testDiscardUpstream() {
+    writeTestData();
+    trackOutput.discardUpstreamSamples(8);
+    assertAllocationCount(10);
+    trackOutput.discardUpstreamSamples(7);
+    assertAllocationCount(9);
+    trackOutput.discardUpstreamSamples(6);
+    assertAllocationCount(8); // Byte not belonging to sample prevents 7.
+    trackOutput.discardUpstreamSamples(5);
+    assertAllocationCount(5);
+    trackOutput.discardUpstreamSamples(4);
+    assertAllocationCount(4);
+    trackOutput.discardUpstreamSamples(3);
+    assertAllocationCount(3);
+    trackOutput.discardUpstreamSamples(2);
+    assertAllocationCount(3); // Byte not belonging to sample prevents 2.
+    trackOutput.discardUpstreamSamples(1);
+    assertAllocationCount(2); // Byte not belonging to sample prevents 1.
+    trackOutput.discardUpstreamSamples(0);
+    assertAllocationCount(1); // Byte not belonging to sample prevents 0.
+    assertReadFormat(false, TEST_FORMAT_2);
+    assertNoSamplesToRead(TEST_FORMAT_2);
+  }
+
+  public void testDiscardUpstreamMulti() {
+    writeTestData();
+    trackOutput.discardUpstreamSamples(4);
+    assertAllocationCount(4);
+    trackOutput.discardUpstreamSamples(0);
+    assertAllocationCount(1); // Byte not belonging to sample prevents 0.
+    assertReadFormat(false, TEST_FORMAT_2);
+    assertNoSamplesToRead(TEST_FORMAT_2);
+  }
+
+  public void testDiscardUpstreamBeforeRead() {
+    writeTestData();
+    trackOutput.discardUpstreamSamples(4);
+    assertAllocationCount(4);
+    assertReadTestData(null, 0, 4);
+    assertReadFormat(false, TEST_FORMAT_2);
+    assertNoSamplesToRead(TEST_FORMAT_2);
+  }
+
+  public void testDiscardUpstreamAfterRead() {
+    writeTestData();
+    assertReadTestData(null, 0, 3);
+    trackOutput.discardUpstreamSamples(8);
+    assertAllocationCount(7);
+    trackOutput.discardUpstreamSamples(7);
+    assertAllocationCount(6);
+    trackOutput.discardUpstreamSamples(6);
+    assertAllocationCount(5); // Byte not belonging to sample prevents 4.
+    trackOutput.discardUpstreamSamples(5);
+    assertAllocationCount(2);
+    trackOutput.discardUpstreamSamples(4);
+    assertAllocationCount(1);
+    trackOutput.discardUpstreamSamples(3);
+    assertAllocationCount(0);
+    assertReadFormat(false, TEST_FORMAT_2);
+    assertNoSamplesToRead(TEST_FORMAT_2);
+  }
+
   // Internal methods.
   // Internal methods.
 
 
   /**
   /**
@@ -293,8 +355,20 @@ public class DefaultTrackOutputTest extends TestCase {
    * @param firstSampleIndex The index of the first sample that's expected to be read.
    * @param firstSampleIndex The index of the first sample that's expected to be read.
    */
    */
   private void assertReadTestData(Format startFormat, int firstSampleIndex) {
   private void assertReadTestData(Format startFormat, int firstSampleIndex) {
+    assertReadTestData(startFormat, firstSampleIndex,
+        TEST_SAMPLE_TIMESTAMPS.length - firstSampleIndex);
+  }
+
+  /**
+   * Asserts correct reading of standard test data from {@code trackOutput}.
+   *
+   * @param startFormat The format of the last sample previously read from {@code trackOutput}.
+   * @param firstSampleIndex The index of the first sample that's expected to be read.
+   * @param sampleCount The number of samples to read.
+   */
+  private void assertReadTestData(Format startFormat, int firstSampleIndex, int sampleCount) {
     Format format = startFormat;
     Format format = startFormat;
-    for (int i = firstSampleIndex; i < TEST_SAMPLE_TIMESTAMPS.length; i++) {
+    for (int i = firstSampleIndex; i < firstSampleIndex + sampleCount; i++) {
       // Use equals() on the read side despite using referential equality on the write side, since
       // Use equals() on the read side despite using referential equality on the write side, since
       // trackOutput de-duplicates written formats using equals().
       // trackOutput de-duplicates written formats using equals().
       if (!TEST_SAMPLE_FORMATS[i].equals(format)) {
       if (!TEST_SAMPLE_FORMATS[i].equals(format)) {

library/core/src/main/java/com/google/android/exoplayer2/extractor/SampleMetadataQueue.java

@@ -111,8 +111,8 @@ import com.google.android.exoplayer2.util.Util;
     Assertions.checkArgument(0 <= discardCount && discardCount <= length);
     Assertions.checkArgument(0 <= discardCount && discardCount <= length);
 
 
     if (discardCount == 0) {
     if (discardCount == 0) {
-      if (absoluteStartIndex == 0) {
-        // length == absoluteStartIndex == 0, so nothing has been written to the queue.
+      if (absoluteStartIndex == 0 && length == 0) {
+        // Nothing has been written to the queue.
         return 0;
         return 0;
       }
       }
       int lastWriteIndex = (relativeEndIndex == 0 ? capacity : relativeEndIndex) - 1;
       int lastWriteIndex = (relativeEndIndex == 0 ? capacity : relativeEndIndex) - 1;