There's a bit of a problem with XFillBitmapItem, which contains a
GraphicObject that can't be swapped because it's a poolable item.

Generally contemptorary hardware has enough RAM that we can easily
increase the cache size to 400M (effectively there's another factor
of 2x), but on legacy 32-bit platforms the address space is getting
scarce, so keep the existing size for those.

Change-Id: I8437f4e8c5421f8ec20e94e4cdf64f867d7760ca