This directory contains files from several different implementations and implementation strategies:
These files implement the current streams spec, plus the more speculative ReadableByteStream, to the extent necessary to support Fetch response bodies. They do not support author-constructed readable streams. They use the normal approach for implementing web-exposed classes, i.e. IDL bindings with C++ implementation. They are now deprecated and will be removed shortly. See https://crbug.com/613435.
These files implement V8 extras based ReadableStream which is currently used.
These files support an old streams spec. They should eventually be removed, but right now XMLHttpRequest and Media Streams Extension code in Blink still depends on them.