- uses a different method of constructor selection that also works on Apple clang < 8.2.
Not in use at the moment, was causing a compiler error on Apple LLVM version 8.0.0 (clang-800.0.42.1). ``` src/mbgl/sprite/sprite_loader.cpp:25:11: error: call to constructor of 'Actor<mbgl::SpriteLoaderWorker>' is ambiguous ```
They will be needed by the DefaultFileSource, something that we also export as public.