Add convenience getPlayer methods to UI components

Issue: #1895

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135211179

library/src/main/java/com/google/android/exoplayer2/ui/PlaybackControlView.java

@@ -128,6 +128,13 @@ public class PlaybackControlView extends FrameLayout {
   }
   }
 
 
   /**
   /**
+   * Returns the player currently being controlled by this view, or null if no player is set.
+   */
+  public ExoPlayer getPlayer() {
+    return player;
+  }
+
+  /**
    * Sets the {@link ExoPlayer} to control.
    * Sets the {@link ExoPlayer} to control.
    *
    *
    * @param player the {@code ExoPlayer} to control.
    * @param player the {@code ExoPlayer} to control.

library/src/main/java/com/google/android/exoplayer2/ui/SimpleExoPlayerView.java

@@ -94,6 +94,13 @@ public final class SimpleExoPlayerView extends FrameLayout {
   }
   }
 
 
   /**
   /**
+   * Returns the player currently set on this view, or null if no player is set.
+   */
+  public SimpleExoPlayer getPlayer() {
+    return player;
+  }
+
+  /**
    * Set the {@link SimpleExoPlayer} to use. The {@link SimpleExoPlayer#setTextOutput} and
    * Set the {@link SimpleExoPlayer} to use. The {@link SimpleExoPlayer#setTextOutput} and
    * {@link SimpleExoPlayer#setVideoListener} method of the player will be called and previous
    * {@link SimpleExoPlayer#setVideoListener} method of the player will be called and previous
    * assignments are overridden.
    * assignments are overridden.