Fixes for retries

- Fix issue in ExoPlayerImpl where the timeline was null'd
  but onTimelineChanged was not fired.
- Add the ability to not reset the timeline. This is useful
  for retries where you know the timeline will be the same
  as it was previously.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135797577

demo/src/main/java/com/google/android/exoplayer2/demo/EventLogger.java

@@ -97,6 +97,9 @@ import java.util.Locale;
 
   @Override
   public void onTimelineChanged(Timeline timeline, Object manifest) {
+    if (timeline == null) {
+      return;
+    }
     int periodCount = timeline.getPeriodCount();
     int windowCount = timeline.getWindowCount();
     Log.d(TAG, "sourceInfo [periodCount=" + periodCount + ", windowCount=" + windowCount);

demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -101,6 +101,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
   }
 
   private Handler mainHandler;
+  private Timeline.Window window;
   private EventLogger eventLogger;
   private SimpleExoPlayerView simpleExoPlayerView;
   private LinearLayout debugRootView;
@@ -115,7 +116,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
   private boolean playerNeedsSource;
 
   private boolean shouldAutoPlay;
-  private boolean shouldRestorePosition;
+  private boolean isTimelineStatic;
   private int playerWindow;
   private long playerPosition;
 
@@ -127,6 +128,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
     shouldAutoPlay = true;
     mediaDataSourceFactory = buildDataSourceFactory(true);
     mainHandler = new Handler();
+    window = new Timeline.Window();
     if (CookieHandler.getDefault() != DEFAULT_COOKIE_MANAGER) {
       CookieHandler.setDefault(DEFAULT_COOKIE_MANAGER);
     }
@@ -147,7 +149,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
   @Override
   public void onNewIntent(Intent intent) {
     releasePlayer();
-    shouldRestorePosition = false;
+    isTimelineStatic = false;
     setIntent(intent);
   }
 
@@ -262,7 +264,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
       player.setVideoDebugListener(eventLogger);
       player.setId3Output(eventLogger);
       simpleExoPlayerView.setPlayer(player);
-      if (shouldRestorePosition) {
+      if (isTimelineStatic) {
         if (playerPosition == C.TIME_UNSET) {
           player.seekToDefaultPosition(playerWindow);
         } else {
@@ -305,7 +307,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
       }
       MediaSource mediaSource = mediaSources.length == 1 ? mediaSources[0]
           : new ConcatenatingMediaSource(mediaSources);
-      player.prepare(mediaSource, !shouldRestorePosition);
+      player.prepare(mediaSource, !isTimelineStatic, !isTimelineStatic);
       playerNeedsSource = false;
       updateButtonVisibilities();
     }
@@ -348,15 +350,11 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
       debugViewHelper.stop();
       debugViewHelper = null;
       shouldAutoPlay = player.getPlayWhenReady();
-      shouldRestorePosition = false;
+      playerWindow = player.getCurrentWindowIndex();
+      playerPosition = C.TIME_UNSET;
       Timeline timeline = player.getCurrentTimeline();
-      if (timeline != null) {
-        playerWindow = player.getCurrentWindowIndex();
-        Timeline.Window window = timeline.getWindow(playerWindow, new Timeline.Window());
-        if (!window.isDynamic) {
-          shouldRestorePosition = true;
-          playerPosition = window.isSeekable ? player.getCurrentPosition() : C.TIME_UNSET;
-        }
+      if (timeline != null && timeline.getWindow(playerWindow, window).isSeekable) {
+        playerPosition = player.getCurrentPosition();
       }
       player.release();
       player = null;
@@ -412,7 +410,8 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
 
   @Override
   public void onTimelineChanged(Timeline timeline, Object manifest) {
-    // Do nothing.
+    isTimelineStatic = timeline != null && timeline.getWindowCount() > 0
+        && !timeline.getWindow(timeline.getWindowCount() - 1, window).isDynamic;
   }
 
   @Override
@@ -501,7 +500,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
         button.setText(label);
         button.setTag(i);
         button.setOnClickListener(this);
-        debugRootView.addView(button);
+        debugRootView.addView(button, debugRootView.getChildCount() - 1);
       }
     }
   }

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

@@ -130,8 +130,8 @@ public interface ExoPlayer {
     /**
      * Called when timeline and/or manifest has been refreshed.
      *
-     * @param timeline The latest timeline.
-     * @param manifest The latest manifest.
+     * @param timeline The latest timeline, or null if the timeline is being cleared.
+     * @param manifest The latest manifest, or null if the manifest is being cleared.
      */
     void onTimelineChanged(Timeline timeline, Object manifest);
 
@@ -247,7 +247,7 @@ public interface ExoPlayer {
 
   /**
    * Prepares the player to play the provided {@link MediaSource}. Equivalent to
-   * {@code prepare(mediaSource, true)}.
+   * {@code prepare(mediaSource, true, true)}.
    */
   void prepare(MediaSource mediaSource);
 
@@ -259,8 +259,11 @@ public interface ExoPlayer {
    * @param resetPosition Whether the playback position should be reset to the default position in
    *     the first {@link Timeline.Window}. If false, playback will start from the position defined
    *     by {@link #getCurrentWindowIndex()} and {@link #getCurrentPosition()}.
+   * @param resetTimeline Whether the timeline and manifest should be reset. Should be true unless
+   *     the player is being prepared to play the same media as it was playing previously (e.g. if
+   *     playback failed and is being retried).
    */
-  void prepare(MediaSource mediaSource, boolean resetPosition);
+  void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetTimeline);
 
   /**
    * Sets whether playback should proceed when {@link #getPlaybackState()} == {@link #STATE_READY}.

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

@@ -101,12 +101,18 @@ import java.util.concurrent.CopyOnWriteArraySet;
 
   @Override
   public void prepare(MediaSource mediaSource) {
-    prepare(mediaSource, true);
+    prepare(mediaSource, true, true);
   }
 
   @Override
-  public void prepare(MediaSource mediaSource, boolean resetPosition) {
-    timeline = null;
+  public void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetTimeline) {
+    if (resetTimeline && (timeline != null || manifest != null)) {
+      timeline = null;
+      manifest = null;
+      for (EventListener listener : listeners) {
+        listener.onTimelineChanged(null, null);
+      }
+    }
     internalPlayer.prepare(mediaSource, resetPosition);
   }
 

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

@@ -420,8 +420,8 @@ public final class SimpleExoPlayer implements ExoPlayer {
   }
 
   @Override
-  public void prepare(MediaSource mediaSource, boolean resetPosition) {
-    player.prepare(mediaSource, resetPosition);
+  public void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetTimeline) {
+    player.prepare(mediaSource, resetPosition, resetTimeline);
   }
 
   @Override