Lock custom observer

Signed-off-by: Alex Saveau <[email protected]>

Author: SUPERCILEX

auth/src/main/java/com/firebase/ui/auth/viewmodel/ResourceObserver.java

@@ -2,13 +2,15 @@
 
 import android.arch.lifecycle.Observer;
 import android.support.annotation.NonNull;
+import android.support.annotation.RestrictTo;
 import android.support.annotation.StringRes;
 
 import com.firebase.ui.auth.data.model.Resource;
 import com.firebase.ui.auth.data.model.State;
 import com.firebase.ui.auth.ui.HelperActivityBase;
 import com.firebase.ui.auth.util.ui.FlowUtils;
 
+@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
 public abstract class ResourceObserver<T> implements Observer<Resource<T>> {
     private final HelperActivityBase mActivity;
     private final int mLoadingMessage;