class WireWeakSyncClientImpl

On completion, all previous StreamProcessor calls have done what they're

going to do server-side, _except_ for processing of data queued using

QueueInputPacket().

The main purpose of this call is to enable the client to wait until

CloseCurrentStream() with release_input_buffers and/or

release_output_buffers set to true to take effect, before the client

allocates new buffers and re-sets-up input and/or output buffers. This

de-overlapping of resource usage can be worthwhile for media buffers

which can consume resource types whose overall pools aren't necessarily

vast in comparison to resources consumed. Especially if a client is

reconfiguring buffers multiple times.

Note that Sync() prior to allocating new media buffers is not alone

sufficient to achieve non-overlap of media buffer resource usage system

wide, but it can be a useful part of achieving that.

The Sync() transits the Output ordering domain and the StreamControl

ordering domain, but not the InputData ordering domain.

This request can be used to avoid hitting kMaxInFlightStreams which is

presently 10. A client that stays

<

= 8 in-flight streams will

comfortably stay under the limit of 10. While the protocol permits

repeated SetInputBufferSettings() and the like, a client that spams the

channel can expect that the channel will just close if the server or the

channel itself gets too far behind.

Allocates 32 bytes of message buffer on the stack. No heap allocation necessary.