Most callers of set_automatic_scrolling_active() also change
m_automatic_scrolling_kind, and it makes it possible to make timer
behavior dependent on the autoscroll kind later.
It's slightly less code, and m_scrubber_in_use is now set correctly
when shift-clicking, keeping the mouse button down, and then
dragging the throbber.
The shift-click brings the scrubber under the cursor, and then
the scrubber_rect().contains() condition is true and both scrubber
drags and shift-click-drags are handled the same naturally.
In order to calculate a thumb size that is a representation
of the visible portion (page) of the content, that information
needs to be taken into account.
You can now #include <AK/Forward.h> to get most of the AK types as
forward declarations.
Header dependency explosion is one of the main contributors to compile
times at the moment, so this is a step towards smaller include graphs.
