re-add WriteReq and CorkedRequest constructors

[mscdex]

This PR is in anticipation of nodejs/node#10558 (do not land this before the node core PR).

Also, this should land before #253 so that the replacements are done in the correct order.

/cc @mcollina

[mcollina]

LGTM

[calvinmetcalf]

so once nodejs/node#10558 lands I'll try merging in this and #253

[calvinmetcalf]

so I've got a couple questions

1. is this that the perf benefits of object literals vs constructors have changed in more recent versions of v8 or is it that better perfing has shown that object literals were better all along
2. why is this beneficial in node core but NOT in readable stream?

have been out of the loop the last week or 2 so sorry if this has been answered already

[mcollina]

is this that the perf benefits of object literals vs constructors have changed in more recent versions of v8 or is it that better perfing has shown that object literals were better all along

Only most recent versions

why is this beneficial in node core but NOT in readable stream?

It will cause a slowdown for older node versions.

[mcollina]

Part of #262

[mcollina]

Merging this have been a mistake. This should be merged when Node.js hits v8.0.0, as the the HTTP changes lands.

[calvinmetcalf]

@mcollina there is a merge conflict here, can you rebase it ?

[mcollina]

we need this for #290. I'll see what I can do but I am traveling this week.

[calvinmetcalf]

ok I can probably do it too, I'm not 100% on it though like how many libraries are using corked writable streams in the hot path and in older node using readable-streams. Wouldn't they also be having similar if not bigger performance issues from using that older node and they'd get bigger benefits from upgrading ?

[mcollina]

Closing as it is now part of #290.