Fix according to review

Author: tom-andersen

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -36,6 +36,7 @@
 import com.google.firebase.firestore.auth.FirebaseAppCheckTokenProvider;
 import com.google.firebase.firestore.auth.FirebaseAuthCredentialsProvider;
 import com.google.firebase.firestore.auth.User;
+import com.google.firebase.firestore.core.ActivityScope;
 import com.google.firebase.firestore.core.AsyncEventListener;
 import com.google.firebase.firestore.core.ComponentProvider;
 import com.google.firebase.firestore.core.DatabaseInfo;
@@ -834,7 +835,15 @@ private ListenerRegistration addSnapshotsInSyncListener(
         };
     AsyncEventListener<Void> asyncListener = new AsyncEventListener<>(userExecutor, eventListener);
     return clientProvider.call(
-        client -> client.addSnapshotsInSyncListener(activity, asyncListener));
+        client -> {
+          client.addSnapshotsInSyncListener(asyncListener);
+          return ActivityScope.bind(
+              activity,
+              () -> {
+                asyncListener.mute();
+                client.removeSnapshotsInSyncListener(asyncListener);
+              });
+        });
   }
 
   <T> T callClient(Function<FirestoreClient, T> call) {

firebase-firestore/src/main/java/com/google/firebase/firestore/core/FirestoreClient.java

@@ -17,7 +17,6 @@
 import static com.google.firebase.firestore.util.Assert.hardAssert;
 
 import android.annotation.SuppressLint;
-import android.app.Activity;
 import android.content.Context;
 import androidx.annotation.Nullable;
 import com.google.android.gms.tasks.Task;
@@ -27,7 +26,6 @@
 import com.google.firebase.firestore.EventListener;
 import com.google.firebase.firestore.FirebaseFirestoreException;
 import com.google.firebase.firestore.FirebaseFirestoreException.Code;
-import com.google.firebase.firestore.ListenerRegistration;
 import com.google.firebase.firestore.LoadBundleTask;
 import com.google.firebase.firestore.TransactionOptions;
 import com.google.firebase.firestore.auth.CredentialsProvider;
@@ -302,16 +300,9 @@ private void initialize(
     }
   }
 
-  public ListenerRegistration addSnapshotsInSyncListener(
-      Activity activity, AsyncEventListener<Void> listener) {
+  public void addSnapshotsInSyncListener(EventListener<Void> listener) {
     verifyNotTerminated();
     asyncQueue.enqueueAndForget(() -> eventManager.addSnapshotsInSyncListener(listener));
-    return ActivityScope.bind(
-        activity,
-        () -> {
-          listener.mute();
-          asyncQueue.enqueueAndForget(() -> eventManager.removeSnapshotsInSyncListener(listener));
-        });
   }
 
   public void loadBundle(InputStream bundleData, LoadBundleTask resultTask) {
@@ -360,6 +351,11 @@ public void deleteAllFieldIndexes() {
     asyncQueue.enqueueAndForget(() -> localStore.deleteAllFieldIndexes());
   }
 
+  public void removeSnapshotsInSyncListener(EventListener<Void> listener) {
+    // `enqueueAndForget` will no-op if client is already terminated.
+    asyncQueue.enqueueAndForget(() -> eventManager.removeSnapshotsInSyncListener(listener));
+  }
+
   private void verifyNotTerminated() {
     if (this.isTerminated()) {
       throw new IllegalStateException("The client has already been terminated");