Simplify timeline test stub class.

Use an actual class for the stub media source instead of an anomymous class.
Allows to call assertReleased() on that class.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=159109143

library/core/src/androidTest/java/com/google/android/exoplayer2/TimelineTest.java

@@ -73,13 +73,24 @@ public class TimelineTest extends TestCase {
   }
 
   /**
-   * Returns a stub {@link MediaSource} with the specified {@link Timeline} in its source info.
+   * Stub media source which returns a provided timeline as source info and keeps track if it is
+   * prepared and released.
    */
-  public static MediaSource stubMediaSourceSourceWithTimeline(final Timeline timeline) {
+  public static class StubMediaSource implements MediaSource {
-    return new MediaSource() {
+    private final Timeline timeline;
+
+    private boolean isPrepared;
+    private volatile boolean isReleased;
+
+    public StubMediaSource(Timeline timeline) {
+      this.timeline = timeline;
+    }
+
     @Override
     public void prepareSource(ExoPlayer player, boolean isTopLevelSource, Listener listener) {
+      assertFalse(isPrepared);
       listener.onSourceInfoRefreshed(timeline, null);
+      isPrepared = true;
     }
 
     @Override
@@ -97,13 +108,17 @@ public class TimelineTest extends TestCase {
 
     @Override
     public void releaseSource() {
+      assertTrue(isPrepared);
+      isReleased = true;
+    }
+
+    public void assertReleased() {
+      assertTrue(isReleased);
     }
-    };
   }
 
   /**
-   * Works in conjunction with {@code stubMediaSourceSourceWithTimeline} to extract the Timeline
+   * Extracts the timeline from a media source.
-   * from a media source.
    */
   public static Timeline extractTimelineFromMediaSource(MediaSource mediaSource) {
     class TimelineListener implements Listener {

library/core/src/androidTest/java/com/google/android/exoplayer2/source/ClippingMediaSourceTest.java

@@ -23,6 +23,7 @@ import com.google.android.exoplayer2.Timeline.Period;
 import com.google.android.exoplayer2.Timeline.Window;
 import com.google.android.exoplayer2.TimelineTest;
 import com.google.android.exoplayer2.TimelineTest.FakeTimeline;
+import com.google.android.exoplayer2.TimelineTest.StubMediaSource;
 import com.google.android.exoplayer2.TimelineTest.TimelineVerifier;
 
 /**
@@ -119,7 +120,7 @@ public final class ClippingMediaSourceTest extends InstrumentationTestCase {
    * Wraps the specified timeline in a {@link ClippingMediaSource} and returns the clipped timeline.
    */
   private static Timeline getClippedTimeline(Timeline timeline, long startMs, long endMs) {
-    MediaSource mediaSource = TimelineTest.stubMediaSourceSourceWithTimeline(timeline);
+    MediaSource mediaSource = new StubMediaSource(timeline);
     return TimelineTest.extractTimelineFromMediaSource(
         new ClippingMediaSource(mediaSource, startMs, endMs));
   }

library/core/src/androidTest/java/com/google/android/exoplayer2/source/ConcatenatingMediaSourceTest.java

@@ -20,6 +20,7 @@ import com.google.android.exoplayer2.ExoPlayer;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.TimelineTest;
 import com.google.android.exoplayer2.TimelineTest.FakeTimeline;
+import com.google.android.exoplayer2.TimelineTest.StubMediaSource;
 import com.google.android.exoplayer2.TimelineTest.TimelineVerifier;
 import junit.framework.TestCase;
 
@@ -101,7 +102,7 @@ public final class ConcatenatingMediaSourceTest extends TestCase {
       Timeline... timelines) {
     MediaSource[] mediaSources = new MediaSource[timelines.length];
     for (int i = 0; i < timelines.length; i++) {
-      mediaSources[i] = TimelineTest.stubMediaSourceSourceWithTimeline(timelines[i]);
+      mediaSources[i] = new StubMediaSource(timelines[i]);
     }
     return TimelineTest.extractTimelineFromMediaSource(
         new ConcatenatingMediaSource(isRepeatOneAtomic, mediaSources));

library/core/src/androidTest/java/com/google/android/exoplayer2/source/LoopingMediaSourceTest.java

@@ -20,6 +20,7 @@ import com.google.android.exoplayer2.ExoPlayer;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.TimelineTest;
 import com.google.android.exoplayer2.TimelineTest.FakeTimeline;
+import com.google.android.exoplayer2.TimelineTest.StubMediaSource;
 import com.google.android.exoplayer2.TimelineTest.TimelineVerifier;
 import junit.framework.TestCase;
 
@@ -33,9 +34,9 @@ public class LoopingMediaSourceTest extends TestCase {
   public LoopingMediaSourceTest() {
     multiWindowTimeline = TimelineTest.extractTimelineFromMediaSource(
         new ConcatenatingMediaSource(
-            TimelineTest.stubMediaSourceSourceWithTimeline(new FakeTimeline(1, 111)),
+            new StubMediaSource(new FakeTimeline(1, 111)),
-            TimelineTest.stubMediaSourceSourceWithTimeline(new FakeTimeline(1, 222)),
+            new StubMediaSource(new FakeTimeline(1, 222)),
-            TimelineTest.stubMediaSourceSourceWithTimeline(new FakeTimeline(1, 333))));
+            new StubMediaSource(new FakeTimeline(1, 333))));
   }
 
   public void testSingleLoop() {
@@ -83,7 +84,7 @@ public class LoopingMediaSourceTest extends TestCase {
    * the looping timeline.
    */
   private static Timeline getLoopingTimeline(Timeline timeline, int loopCount) {
-    MediaSource mediaSource = TimelineTest.stubMediaSourceSourceWithTimeline(timeline);
+    MediaSource mediaSource = new StubMediaSource(timeline);
     return TimelineTest.extractTimelineFromMediaSource(
         new LoopingMediaSource(mediaSource, loopCount));
   }