(ChromeOS does not rely on X but rather has its own windowing system developed by Google.)
Writers hopeful about Wayland love to talk about how Gnome or KDE already supports of will soon support Wayland, despite the fact that for a desktop/laptop OS, support from one of the major browsers is much more important than support from Gnome or KDE. (Yes, I know that Gnome includes a web browser: that browser will not work however with all or even most of the sites a typical user needs to visit.) And it is far from certain whether any of the major browsers will ever run on Wayland (without XWayland or some other large X-compatibility library that relies on X) whereas of course one of the major open-source browsers already runs reliably on the windowing system and low-level graphical libraries in ChromeOS.