The default limit (at least on Linux) causes us to run out of file
descriptors at around 15 tabs. Increase this limit to 8k. This is a
rather arbitrary number, but matches the limit set by Chrome.
This allows main UI processes created while there is a currently
running one to request a new tab or a new window with the initial urls
provided on the command line. This matches (almost) the behavior of
Chromium and Firefox.
Add a new IPC protocol between two UI processes. The main UI process
will create an IPC server socket, while secondary UI processes will
connect to that socket and send over the URLs and action it wants the
main process to take.
