Presto wouldn't be so memory efficient on today's web; web applications typically ran into plenty of places where memory consumption was worse in Presto versus WebKit, for example. (A simple example here is that each DOM Node was larger in Presto than any other browser, if I'm not forgetting.)
But ultimately a lot of this comes down to different considerations: when the majority of your revenue comes from companies who care about running on limited devices, of _course_ the company invested more in running well on them. And I wouldn't hold up Presto as a great example of modularity or the ability to embed the rendering engine in other projects.
But ultimately a lot of this comes down to different considerations: when the majority of your revenue comes from companies who care about running on limited devices, of _course_ the company invested more in running well on them. And I wouldn't hold up Presto as a great example of modularity or the ability to embed the rendering engine in other projects.