a #GAsyncResult
a location to place the contents of the file
a location to place the current entity tag for the file, or null if the entity tag is not needed
true if the load was successful. If false and error is present, it will be set appropriately.
Finishes an asynchronous load of the file's contents. The contents are placed in contents, and length is set to the size of the contents string. The contents should be freed with glib.global.gfree when no longer needed. If etag_out is present, it will be set to the new entity tag for the file.