This might be theoretically possible, but I don't think it's been done yet. All the fast browsers so far take a while to build.

It's worthwhile to note that Blink (v. the whole of Chromium) has had its build time quintuple in the past four years or so, and its starting point was far slower than Presto (which may or may not qualify as "fast" in people's books, depending on what features you care about).

Show me how, then.

I didn't say I know how to do it. And I didn't say it's easy. Yes, currently we have fast browser and slow compilation. Just let's not assume situation can't be improved at all.