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.
GException on failure.
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 g_free() when no longer needed. If @etag_out is present, it will be set to the new entity tag for the @file.