HTTP2 functionality requires changes to work with TTD #372

• Version: master
• Platform: all
• Subsystem: TTD, http2

Some changes to http2 require updates to support TTD properly: the upstream commit is
nodejs/node@e46ae99 and will need similar changes to those in #194, or otherwise will require a change in how we handle this scenario.

I spoke with @mrkmarron and he had this to offer:

This aliasing a backing array through a C++ and JS variable just seems like a terrible idea to me and I was hoping that it was a one off optimization. However, it looks like it is spreading so I think we may want to do a bit of work to create an API that we can use to track these cases and which will not create a lot of merge conflicts going forward. E.g. add a few macros for CREATE_ALIASED_BUFFER() and MODIFY_ALIASED_BUFFER() where we can hide the rest of the changes behind them (and maybe even try to upstream as nops).