Fix bug in ActionSchedule.

When having a repeat() action and another subsequent action,
the next action should only be scheduled once (and not repeatedly).
Thus, the "next" pointer in the repeated action needs to be nulled
in the first iteration to prevent repeated scheduling of the next action.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=168202212

testutils/src/main/java/com/google/android/exoplayer2/testutil/ActionSchedule.java

@@ -18,7 +18,6 @@ package com.google.android.exoplayer2.testutil;
 import android.os.Handler;
 import android.view.Surface;
 import com.google.android.exoplayer2.C;
-import com.google.android.exoplayer2.ExoPlayer;
 import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.SimpleExoPlayer;
 import com.google.android.exoplayer2.Timeline;
@@ -211,7 +210,7 @@ public final class ActionSchedule {
 
     /**
      * Schedules a new source preparation action to be executed.
-     * @see ExoPlayer#prepare(MediaSource, boolean, boolean).
+     * @see com.google.android.exoplayer2.ExoPlayer#prepare(MediaSource, boolean, boolean).
      *
      * @return The builder, for convenience.
      */
@@ -350,7 +349,13 @@ public final class ActionSchedule {
     public void run() {
       action.doActionAndScheduleNext(player, trackSelector, surface, mainHandler, next);
       if (repeatIntervalMs != C.TIME_UNSET) {
-        clock.postDelayed(mainHandler, this, repeatIntervalMs);
+        clock.postDelayed(mainHandler, new Runnable() {
+            @Override
+            public void run() {
+              action.doActionAndScheduleNext(player, trackSelector, surface, mainHandler, null);
+              clock.postDelayed(mainHandler, this, repeatIntervalMs);
+            }
+          }, repeatIntervalMs);
       }
     }