Opt uncontroversial bits of the main demo app into unstable APIs

None of these components/features are planned to be part of the initial
stable API, so these suppressions will need to be in place when we
enable the warnings.

PiperOrigin-RevId: 437256731

demos/main/src/main/java/androidx/media3/demo/main/DemoDownloadService.java

@@ -20,6 +20,7 @@ import static androidx.media3.demo.main.DemoUtil.DOWNLOAD_NOTIFICATION_CHANNEL_I
 import android.app.Notification;
 import android.content.Context;
 import androidx.annotation.Nullable;
+import androidx.annotation.OptIn;
 import androidx.media3.common.util.NotificationUtil;
 import androidx.media3.common.util.Util;
 import androidx.media3.exoplayer.offline.Download;
@@ -32,6 +33,7 @@ import androidx.media3.exoplayer.scheduler.Scheduler;
 import java.util.List;
 
 /** A service for downloading media. */
+@OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
 public class DemoDownloadService extends DownloadService {
 
   private static final int JOB_ID = 1;

demos/main/src/main/java/androidx/media3/demo/main/DemoUtil.java

@@ -16,6 +16,7 @@
 package androidx.media3.demo.main;
 
 import android.content.Context;
+import androidx.annotation.OptIn;
 import androidx.media3.database.DatabaseProvider;
 import androidx.media3.database.StandaloneDatabaseProvider;
 import androidx.media3.datasource.DataSource;
@@ -71,6 +72,7 @@ public final class DemoUtil {
     return BuildConfig.USE_DECODER_EXTENSIONS;
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   public static RenderersFactory buildRenderersFactory(
       Context context, boolean preferExtensionRenderer) {
     @DefaultRenderersFactory.ExtensionRendererMode
@@ -116,6 +118,7 @@ public final class DemoUtil {
     return dataSourceFactory;
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   public static synchronized DownloadNotificationHelper getDownloadNotificationHelper(
       Context context) {
     if (downloadNotificationHelper == null) {
@@ -135,6 +138,7 @@ public final class DemoUtil {
     return downloadTracker;
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   private static synchronized Cache getDownloadCache(Context context) {
     if (downloadCache == null) {
       File downloadContentDirectory =
@@ -146,6 +150,7 @@ public final class DemoUtil {
     return downloadCache;
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   private static synchronized void ensureDownloadManagerInitialized(Context context) {
     if (downloadManager == null) {
       downloadManager =
@@ -160,6 +165,7 @@ public final class DemoUtil {
     }
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   private static synchronized DatabaseProvider getDatabaseProvider(Context context) {
     if (databaseProvider == null) {
       databaseProvider = new StandaloneDatabaseProvider(context);
@@ -177,6 +183,7 @@ public final class DemoUtil {
     return downloadDirectory;
   }
 
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   private static CacheDataSource.Factory buildReadOnlyCacheDataSource(
       DataSource.Factory upstreamFactory, Cache cache) {
     return new CacheDataSource.Factory()

demos/main/src/main/java/androidx/media3/demo/main/DownloadTracker.java

@@ -23,6 +23,7 @@ import android.net.Uri;
 import android.os.AsyncTask;
 import android.widget.Toast;
 import androidx.annotation.Nullable;
+import androidx.annotation.OptIn;
 import androidx.annotation.RequiresApi;
 import androidx.fragment.app.FragmentManager;
 import androidx.media3.common.DrmInitData;
@@ -53,6 +54,7 @@ import java.util.HashMap;
 import java.util.concurrent.CopyOnWriteArraySet;
 
 /** Tracks media that has been downloaded. */
+@OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
 public class DownloadTracker {
 
   /** Listens for changes in the tracked downloads. */

demos/main/src/main/java/androidx/media3/demo/main/SampleChooserActivity.java

@@ -41,6 +41,7 @@ import android.widget.ImageButton;
 import android.widget.TextView;
 import android.widget.Toast;
 import androidx.annotation.Nullable;
+import androidx.annotation.OptIn;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.media3.common.MediaItem;
 import androidx.media3.common.MediaItem.ClippingConfiguration;
@@ -120,6 +121,7 @@ public class SampleChooserActivity extends AppCompatActivity
   }
 
   /** Start the download service if it should be running but it's not currently. */
+  @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
   private void startDownloadService() {
     // Starting the service in the foreground causes notification flicker if there is no scheduled
     // action. Starting it in the background throws an exception if the app is in the background too
@@ -274,6 +276,7 @@ public class SampleChooserActivity extends AppCompatActivity
 
     private boolean sawError;
 
+    @OptIn(markerClass = androidx.media3.common.util.UnstableApi.class)
     @Override
     protected List<PlaylistGroup> doInBackground(String... uris) {
       List<PlaylistGroup> result = new ArrayList<>();