Bug 239496

Currently, the RemoteRenderingBackendProxy::DidCreateWakeUpSemaphoreForDisplayListStream() message is dispatched in the RemoteRenderingBackend constructor before the underlying connection is open. The connection exists, it's valid, just not open, so the message isn't sent but it's still kept in the outgoing messages queue. There's no other message dispatched on this connection afterwards, meaning the queue doesn't get flushed. So the initial message is never sent, which then causes problems down the line in GPUProcess execution. It's possible to rework things so that the message is sent after the connection is opened, but there's also the question of whether the Unix implementation of IPC::Connection should handle this situation somewhat better.