Otherwise even a trivial test document renders extremely badly, just
the top row of text in tiles here and there. Go figure. Maybe the code
thinks the document "window" is of some ridiculous 1x1 size or
something if the resize timer isn't used? Also, the resize timer
handler calls paint functionality.

I wonder how we can be sure that the resize timer happens to fire
during the rendering a tile, though? Surely if the tile rendering call
returns before the timer fires, whatever essential thing it is that
the timer needs to do, doesn't happen. Maybe this then explains the
blank tiles I occasionally see? On the other hand, when I see them,
they don't appear randomly, but it's always the same tile that shows
up blank.

Change-Id: If5e6854d8846fb0b7bea15547a326bd77f23987b