It is used as const and also fixes a build issue on iOS: ``` Non-const lvalue reference to type ‘mbgl::OfflineRegion’ cannot bind to a temporary of type ‘typename remove_reference<OfflineRegion &>::type’ (aka ‘mbgl::OfflineRegion’) ```
It is used as const and also fixes a build issue on iOS: ``` Non-const lvalue reference to type ‘mbgl::OfflineRegion’ cannot bind to a temporary of type ‘typename remove_reference<OfflineRegion &>::type’ (aka ‘mbgl::OfflineRegion’) ```