Vertical viewport size regression in Ico's branch (nw.js 0.24.4)

@ico, unfortunately, it seems that I have found another, less obvious, "old-nw.js" regression in your branch. Using nw.js 0.24.4 on Linux (Manjaro), the viewport of a fully visible canvas (i.e., without scrollbars, and with the entire canvas fitting well into the visible area) seems slightly too large (at least in the vertical direction). The observable result is that, even though the window has no scrollbars, you can wiggle the mousewheel and have the window scroll a little amount in the vertical direction. You can easily reproduce this using the "about" window with the current master (rev. dd632b2d) built against nw.js 0.22.4. The following little screencast shows what I mean:

I can make this go away by going back to rev. 11f6610d (before your branch got merged back in). The problem also goes away with the current master, when using nw.js 0.47.0-beta1 instead of our baseline 0.24.4. So it seems fairly obvious to me that it's in fact a regression in your branch with respect to nw.js 0.24.4.