Add support for setting companion ad slots

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205373398

RELEASENOTES.md

@@ -13,8 +13,10 @@
 * DRM:
   * Allow DrmInitData to carry a license server URL
     ([#3393](https://github.com/google/ExoPlayer/issues/3393)).
-* IMA: Fix behavior when creating/releasing the player then releasing
+* IMA:
+  * Fix behavior when creating/releasing the player then releasing
     `ImaAdsLoader` ([#3879](https://github.com/google/ExoPlayer/issues/3879)).
+  * Add support for setting slots for companion ads.
 * Fix issue playing DRM protected streams on Asus Zenfone 2
   ([#4403](https://github.com/google/ExoPlayer/issues/4413)).
 * Add support for multiple audio and video tracks in MPEG-PS streams

extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java

@@ -38,6 +38,7 @@ import com.google.ads.interactivemedia.v3.api.AdsManager;
 import com.google.ads.interactivemedia.v3.api.AdsManagerLoadedEvent;
 import com.google.ads.interactivemedia.v3.api.AdsRenderingSettings;
 import com.google.ads.interactivemedia.v3.api.AdsRequest;
+import com.google.ads.interactivemedia.v3.api.CompanionAdSlot;
 import com.google.ads.interactivemedia.v3.api.ImaSdkFactory;
 import com.google.ads.interactivemedia.v3.api.ImaSdkSettings;
 import com.google.ads.interactivemedia.v3.api.player.ContentProgressProvider;
@@ -62,6 +63,7 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -396,6 +398,17 @@ public final class ImaAdsLoader extends Player.DefaultEventListener implements A
   }
 
   /**
+   * Sets the slots for displaying companion ads. Individual slots can be created using {@link
+   * ImaSdkFactory#createCompanionAdSlot()}.
+   *
+   * @param companionSlots Slots for displaying companion ads.
+   * @see AdDisplayContainer#setCompanionSlots(Collection)
+   */
+  public void setCompanionSlots(Collection<CompanionAdSlot> companionSlots) {
+    adDisplayContainer.setCompanionSlots(companionSlots);
+  }
+
+  /**
    * Requests ads, if they have not already been requested. Must be called on the main thread.
    *
    * <p>Ads will be requested automatically when the player is prepared if this method has not been