Code review comment for lp:~raof/mir/the-least-dirty-thing

Alright, still needs conversion to signed ints though. Like in:
232 + virtual geometry::Point surface_to_screen(std::shared_ptr<frontend::Surface> surface,
233 + uint32_t x, uint32_t y) = 0;

Even local coordinates can go negative -- Consider what happens when you drag something like a scroll bar or image. The scrolling keeps responding even when the pointer itself is out of the window (so could be in negative coordinates).