> If you manage to make a single tab commit that much memory as a delta without Flash (remember, 13 MB to > 400 MB) please screenshot about:memory and get back to me.
I can understand this as a weak prediction, but it certainly doesn't work as a strong one. I can trivially make a tab use over a gigabyte of memory in recent Chromium by creating a gazillion nested objects in JavaScript. (I just did, in fact. If you really want the screenshot and/or source, say so and I'll post it somewhere.) Absent some default limit in V8 that I haven't encountered, I could presumably make it use unbounded memory. I can also create apparently-unbounded latency in a single tab's UI this way, by chewing up CPU in blocking JavaScript code, though this will eventually trigger the “page seems unresponsive” dialog box.
I would also tend to expect an exploit to potentially abuse the JavaScript engine by straining its limits, including things like pouring a large number of identical objects onto the heap to fill memory with exploitable patterns.