ForChunkedEncoding vector as static rather than instance

[benaadams]

_vectorCRs only needs to be allocated once rather than per object

[halter73]

There be dragons hiding behind even the safest seeming changes. Look at all the ChunkedRequestsTests that failed on AppVeyor: https://ci.appveyor.com/project/aspnet-ci/kestrelhttpserver/build/1.0.1646/tests

It turns out that your change causes an InvalidProgramException to be thrown when ForChunkedEncoding is initialized on desktop CLR when Vector.IsHardwareAccelerated == True.

Interestingly if you add a second static vector to the ForChunkedEncoding everything seems to work correctly. This might be why we haven't seen this issue in Frame. This doesn't repro on my laptop since I don't get hardware acceleration of the desktop framework, but @CesarBS can repro it on his machine. We're looking into filing an issue with a simplified repo to dotnet.

[benaadams]

@halter73 hmm that rings a bell... dab1a1f

[benaadams]

Probably needs a comment on that line; I git blame myself 😞

[benaadams]

Can't find any issue I raised for it either 👎

[cesarblum]

It's super easy to repro. Filed https://github.com/dotnet/corefx/issues/8825.

[halter73]

While we could do something adventurous like adding another static Vector to ForChunkedEncoding, I think we just add a comment for now. #877