When we create the first page in the default context in headless mode on mac,
it gets NSWindow that is "not visible". Although we call [window setIsVisible:YES],
later on window.isVisible still returns NO.
We create our offscreen "headless" NSWindow directly from applicationDidFinishLaunching:.
Experiments show that delaying this by 100ms makes everything work. As a symptom,
we get applicationDidUnhide: notification that does not happen when we create the window
immediately.
Perhaps, we create the window too early, and there is some essential initialization
that happens after applicationDidFinishLaunching:. However, if we call
[NSApp activateIgnoringOtherApps:YES] like we do in headful mode, everything works.
The only solution that worked so far is creating the first page after a timeout.
