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Previously, the CDP socket was added to the worker's multi and fully owned
by the worker. While this is simple, it introduced some issues:
1 - Cannot detect a disconnected client during JS processing ( for(;;) )
2 - A blocked worker can cause back-pressure that blocks the client. This can
cause a deadlock if the worker is blocked waiting for a CDP message
In addition to these 2 problems, there was 1 other serious CDP-related issue:
arbitrary CDP messages could be processed during JavaScript callback. For
example, a Worker calls importScripts while request interception is enabled,
this requires us to tick the HttpClient waiting for the interception response.
But, a client could sent Target.closeTarget, which we'd process and delete the
frame..all while importScripts is still blocked. Assuming importScripts unblocks
everything is a big UAF since the frame (and its workers) were cleared from
closeTarget.
The CDP socket is now read from the network (main) thread and an OTP-style
mailbox is used. The network thread posts message to the Worker's inbox and
signals it to wakeup. This solves #1 and #2. It doesn't directly solve the
reentrancy issue, but it provides the foundation. Specifically, in introduces
a queue for of CDP message and more control over when/how that queue is
processed. At "safe points" (Runner.tick, HttpClient.tick), any message can
be processed. But, when inside a JavaScript callback, we can process only non-
destructive/mutating message. Specifically, we can process only messages related
to request interception.