RFC: IpcSharedMemoryVec an appendable data structure which can be shared via a reader

[Narfinger]

This implements IpcSharedMemoryVec (similar to IpcSharedMemory).
This is an OS backed storage of a collection of bytes where we can add bytes to it.
We can access the bytes back with an IpcSharedMemoryIndex. Access is also facilitated with a IpcSharedMemoryVec::reader() method
which can be send over an ipc channel.

Currently this is an RFC because of two reasons:

• IpcSharedMemoryIndex should be serialize/deserialize so we can actually send it.
• Only the Unix implementation was implemented (and tested via tests and in servo context). Other implementations will follow.

Signed-off-by: Narfinger [email protected]

[sagudev]

Hm, I am not sure that would work without anykind of cross process sync mechanism (Is that the reason for closing PR?).

[Narfinger]

Sorry, closed it by accident.
I think the synchronization will be done via the index. You can only access the storage if you have the index which enforces that it exists in the table. And because we never remove any elements this should be safe.