A MessagePort can be transferred while it already has local queued
state such as incoming messages drained from its transport,
outgoing messages posted before a transport exists, and a pending
shutdown to apply once the port is enabled.
Serialize and restore that state as part of transfer so it moves with
the port instead of being left behind on the old transport.
Also mark transports that are being transferred so shutdown of the old
endpoint during handoff is not reported as peer EOF. That shutdown is
part of moving the transport to the new owner, not peer disconnected.
Co-Authored-By: Alexander Kalenik <kalenik.aliaksandr@gmail.com>
When a message is posted to multiple ports at once, the order in which
the callbacks for these messages are invoked is non-deterministic.
To account for this, the test has been rewritten to accumulate logs
for each port separately, and then print them grouped by port.
The way this test was written didn't guarantee a deterministic message
order, resulting in different output in Chromium and Firefox. This
change slightly rearranges the message order to make it deterministic.
This change is necessary as a prepartion for upcoming change that makes
MessagePort post messages from a separate thread, which would've
revealed the non-deterministic message order.
This is to allow future changes to do cross-process MessagePorts in an
implementation-agnostic way. Add some tests for this behavior.
Delivering messages that were posted to a MessagePort just before it was
transferred is not yet implemented still.
