Update PlayerNotficationManager to set PendingIntent.FLAG_IMMUTABLE on its Broadcast intent.

In Android 12 mutability flags have to be set on PendingIntents. If they
are not, and the app targets Android 12, then the app will be crashed by
the system.

PiperOrigin-RevId: 373427591

RELEASENOTES.md

 # Release notes
 # Release notes
 
 
+### dev-v2 (not yet released)
+
+*   UI:
+    *   Add `PendingIntent.FLAG_IMMUTABLE` flag when creating a broadcast intent
+        in `PlayerNotificationManager`. This is required to avoid an error on
+        Android 12.
+
 ### 2.14.1 (2021-06-11)
 ### 2.14.1 (2021-06-11)
 
 
 *   Core Library:
 *   Core Library:

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

@@ -1598,8 +1598,15 @@ public class PlayerNotificationManager {
       String action, Context context, int instanceId) {
       String action, Context context, int instanceId) {
     Intent intent = new Intent(action).setPackage(context.getPackageName());
     Intent intent = new Intent(action).setPackage(context.getPackageName());
     intent.putExtra(EXTRA_INSTANCE_ID, instanceId);
     intent.putExtra(EXTRA_INSTANCE_ID, instanceId);
-    return PendingIntent.getBroadcast(
-        context, instanceId, intent, PendingIntent.FLAG_UPDATE_CURRENT);
+
+    int pendingFlags;
+    if (Util.SDK_INT >= 23) {
+      pendingFlags = PendingIntent.FLAG_UPDATE_CURRENT | PendingIntent.FLAG_IMMUTABLE;
+    } else {
+      pendingFlags = PendingIntent.FLAG_UPDATE_CURRENT;
+    }
+
+    return PendingIntent.getBroadcast(context, instanceId, intent, pendingFlags);
   }
   }
 
 
   @SuppressWarnings("nullness:argument.type.incompatible")
   @SuppressWarnings("nullness:argument.type.incompatible")