Add ExoPlayer.retry convenience method

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211463309

RELEASENOTES.md

@@ -7,8 +7,9 @@
   `compileOptions { targetCompatibility JavaVersion.VERSION_1_8 }` to their
   gradle settings to ensure bytecode compatibility.
 * Set `compileSdkVersion` and `targetSdkVersion` to 28.
-* Added support for automatic audio focus handling via
+* Support for automatic audio focus handling via
   `SimpleExoPlayer.setAudioAttributes`.
+* Added `ExoPlayer.retry` convenience method.
 * Add `AudioListener` for listening to changes in audio configuration during
   playback ([#3994](https://github.com/google/ExoPlayer/issues/3994)).
 * Add `LoadErrorHandlingPolicy` to allow configuration of load error handling

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java

@@ -188,6 +188,12 @@ public interface ExoPlayer extends Player {
    */
   Looper getApplicationLooper();
 
+  /**
+   * Retries a failed or stopped playback. Does nothing if the player has been reset, or if playback
+   * has not failed or been stopped.
+   */
+  void retry();
+
   /**
    * Prepares the player to play the provided {@link MediaSource}. Equivalent to
    * {@code prepare(mediaSource, true, true)}.

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -65,6 +65,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
   private final Timeline.Period period;
   private final ArrayDeque<PlaybackInfoUpdate> pendingPlaybackInfoUpdates;
 
+  private MediaSource mediaSource;
   private boolean playWhenReady;
   private boolean internalPlayWhenReady;
   private @RepeatMode int repeatMode;
@@ -191,14 +192,23 @@ import java.util.concurrent.CopyOnWriteArraySet;
     return playbackError;
   }
 
+  @Override
+  public void retry() {
+    if (mediaSource != null
+        && (playbackError != null || playbackInfo.playbackState == Player.STATE_IDLE)) {
+      prepare(mediaSource, /* resetPosition= */ false, /* resetState= */ false);
+    }
+  }
+
   @Override
   public void prepare(MediaSource mediaSource) {
-    prepare(mediaSource, true, true);
+    prepare(mediaSource, /* resetPosition= */ true, /* resetState= */ true);
   }
 
   @Override
   public void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetState) {
     playbackError = null;
+    this.mediaSource = mediaSource;
     PlaybackInfo playbackInfo =
         getResetPlaybackInfo(
             resetPosition, resetState, /* playbackState= */ Player.STATE_BUFFERING);
@@ -384,6 +394,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
   public void stop(boolean reset) {
     if (reset) {
       playbackError = null;
+      mediaSource = null;
     }
     PlaybackInfo playbackInfo =
         getResetPlaybackInfo(
@@ -410,6 +421,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
     Log.i(TAG, "Release " + Integer.toHexString(System.identityHashCode(this)) + " ["
         + ExoPlayerLibraryInfo.VERSION_SLASHY + "] [" + Util.DEVICE_DEBUG_INFO + "] ["
         + ExoPlayerLibraryInfo.registeredModules() + "]");
+    mediaSource = null;
     internalPlayer.release();
     eventHandler.removeCallbacksAndMessages(null);
   }

library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java

@@ -832,6 +832,14 @@ public class SimpleExoPlayer
     return player.getPlaybackError();
   }
 
+  @Override
+  public void retry() {
+    if (mediaSource != null
+        && (getPlaybackError() != null || getPlaybackState() == Player.STATE_IDLE)) {
+      prepare(mediaSource, /* resetPosition= */ false, /* resetState= */ false);
+    }
+  }
+
   @Override
   public void prepare(MediaSource mediaSource) {
     prepare(mediaSource, /* resetPosition= */ true, /* resetState= */ true);
@@ -839,14 +847,12 @@ public class SimpleExoPlayer
 
   @Override
   public void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetState) {
-    if (this.mediaSource != mediaSource) {
     if (this.mediaSource != null) {
       this.mediaSource.removeEventListener(analyticsCollector);
       analyticsCollector.resetForNewMediaSource();
     }
-      mediaSource.addEventListener(eventHandler, analyticsCollector);
     this.mediaSource = mediaSource;
-    }
+    mediaSource.addEventListener(eventHandler, analyticsCollector);
     @AudioFocusManager.PlayerCommand
     int playerCommand = audioFocusManager.handlePrepare(getPlayWhenReady());
     updatePlayWhenReady(getPlayWhenReady(), playerCommand);
@@ -949,8 +955,10 @@ public class SimpleExoPlayer
     player.stop(reset);
     if (mediaSource != null) {
       mediaSource.removeEventListener(analyticsCollector);
-      mediaSource = null;
       analyticsCollector.resetForNewMediaSource();
+      if (reset) {
+        mediaSource = null;
+      }
     }
     audioFocusManager.handleStop();
     currentCues = Collections.emptyList();
@@ -969,6 +977,7 @@ public class SimpleExoPlayer
     }
     if (mediaSource != null) {
       mediaSource.removeEventListener(analyticsCollector);
+      mediaSource = null;
     }
     bandwidthMeter.removeEventListener(analyticsCollector);
     currentCues = Collections.emptyList();

testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java

@@ -79,6 +79,11 @@ public abstract class StubExoPlayer implements ExoPlayer {
     throw new UnsupportedOperationException();
   }
 
+  @Override
+  public void retry() {
+    throw new UnsupportedOperationException();
+  }
+
   @Override
   public void prepare(MediaSource mediaSource) {
     throw new UnsupportedOperationException();