Very interesting, but I can't quite rap my head around the idea. Aren't the protocols and the execution engine the plattform on which a browser is built? I find it very interesting to think about it what the minimal executable code is and how we ship it over the wire. Chrome was originally an OS as well as a browser (that's how I understand the history).
I'm not sure I understand what you mean by "Aren't the protocols and the execution engine the plattform on which a browser is built?". But I'll try to elaborate.
Chrome is built on the Content API. So it's a whole lot of C++ and GUI code on top of an API that lets you create a view and display web contents in it. The ExoBrowser wraps this Content API (part of it for now) into a JS API so that you can do all the GUI and specific browser code in Javascript instead of C++.
Additionally Chrome is not really an OS, Chrome OS is an "OS" (more a window system on top of Linux) based on Aura (View Management, kind of like GTK) and Chrome to run the apps.
