Track DeathNotifier cookie lifetime

Keep a set of cookies to signal when the DeathNotifier cookie is valid.

Test: cd frameworks/av/media/libmediaplayerservice && atest -p
Test: atest CtsCameraTestCases:android.hardware.camera2.cts.RecordingTest
Test: adb shell kill -9 `pid media.swcodec` # during RecordingTest
Bug: 319210610
Change-Id: Id113b8af0708c3f93e6ddef90751692ac0f32855
diff --git a/media/libmediaplayerservice/DeathNotifier.h b/media/libmediaplayerservice/DeathNotifier.h
index 24e45a3..0fd7c65 100644
--- a/media/libmediaplayerservice/DeathNotifier.h
+++ b/media/libmediaplayerservice/DeathNotifier.h
@@ -37,10 +37,11 @@
     DeathNotifier(DeathNotifier&& other);
     ~DeathNotifier();
 
+    class DeathRecipient;
+
 private:
     std::variant<std::monostate, sp<IBinder>, sp<HBase>, ::ndk::SpAIBinder> mService;
 
-    class DeathRecipient;
     sp<DeathRecipient> mDeathRecipient;
 };