Provide an overlay FrameLayout in SimpleExoPlayerView.

This can be used by the app for showing arbitrary UI on top of the player (for
example, UI elements associated with an ad).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=138610733

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

@@ -141,6 +141,12 @@ import java.util.List;
  *        <li>Type: {@link View}</li>
  *       </ul>
  *   </li>
+ *   <li><b>{@code exo_overlay}</b> - A {@link FrameLayout} positioned on top of the player which
+ *       the app can access via {@link #getOverlayFrameLayout()}, provided for convenience.
+ *       <ul>
+ *        <li>Type: {@link FrameLayout}</li>
+ *       </ul>
+ *   </li>
  * </ul>
  * <p>
  * All child views are optional and so can be omitted if not required, however where defined they
@@ -167,6 +173,7 @@ public final class SimpleExoPlayerView extends FrameLayout {
   private final SubtitleView subtitleView;
   private final PlaybackControlView controller;
   private final ComponentListener componentListener;
+  private final FrameLayout overlayFrameLayout;
 
   private SimpleExoPlayer player;
   private boolean useController;
@@ -231,6 +238,9 @@ public final class SimpleExoPlayerView extends FrameLayout {
       surfaceView = null;
     }
 
+    // Overlay frame layout.
+    overlayFrameLayout = (FrameLayout) findViewById(R.id.exo_overlay);
+
     // Artwork view.
     artworkView = (ImageView) findViewById(R.id.exo_artwork);
     this.useArtwork = useArtwork && artworkView != null;
@@ -421,15 +431,26 @@ public final class SimpleExoPlayerView extends FrameLayout {
   }
 
   /**
-   * Get the view onto which video is rendered. This is either a {@link SurfaceView} (default)
+   * Gets the view onto which video is rendered. This is either a {@link SurfaceView} (default)
    * or a {@link TextureView} if the {@code use_texture_view} view attribute has been set to true.
    *
-   * @return either a {@link SurfaceView} or a {@link TextureView}.
+   * @return Either a {@link SurfaceView} or a {@link TextureView}.
    */
   public View getVideoSurfaceView() {
     return surfaceView;
   }
 
+  /**
+   * Gets the overlay {@link FrameLayout}, which can be populated with UI elements to show on top of
+   * the player.
+   *
+   * @return The overlay {@link FrameLayout}, or {@code null} if the layout has been customized and
+   *     the overlay is not present.
+   */
+  public FrameLayout getOverlayFrameLayout() {
+    return overlayFrameLayout;
+  }
+
   @Override
   public boolean onTouchEvent(MotionEvent ev) {
     if (!useController || player == null || ev.getActionMasked() != MotionEvent.ACTION_DOWN) {

library/src/main/res/layout/exo_simple_player_view.xml

@@ -44,4 +44,8 @@
       android:layout_width="match_parent"
       android:layout_height="match_parent"/>
 
+  <FrameLayout android:id="@id/exo_overlay"
+      android:layout_width="match_parent"
+      android:layout_height="match_parent"/>
+
 </FrameLayout>

library/src/main/res/values/ids.xml

@@ -19,6 +19,7 @@
   <item name="exo_subtitles" type="id"/>
   <item name="exo_artwork" type="id"/>
   <item name="exo_controller_placeholder" type="id"/>
+  <item name="exo_overlay" type="id"/>
   <item name="exo_play" type="id"/>
   <item name="exo_pause" type="id"/>
   <item name="exo_rew" type="id"/>