WT-4447, there is now a redundancy in information and action. With the io_capacity configuration setting, there is a background thread that walks the file handles, in the os_common code. The file handle now contains a written field that is incremented when wt_write is called and cleared when the handle is sync'ed by the capacity background thread.
Similarly, there is support for os_cache_dirty_max and os_cache_max settings on a table. When data is written to a table, the block manager code increments block->os_cache_dirty and will sync the file handle associated with that table.
That is now the same/very similar information being kept in two locations. The block manager code should be modified to use or call into the file handle code to use its mechanism.