LibGUI: Handle GUI::Window non-volatile backing store issues better

Instead of crashing when we can't make the back buffer non-volatile,
we now transition the window into single-buffered mode instead
(assuming it was originally in double-buffered mode.)

This reduces GUI fidelity a bit (by potentially making windows flicker
during repaint) but since it's only triggered in low-memory conditions,
it seems like a reasonable thing to sacrifice in order for the system
to carry on.

This patch also stops us from allocating entirely new backing stores
after the old ones were purged. If they were purged but reallocated
just fine, there's no need to allocate new memory again. We already
have fresh zero-filled pages in the existing bitmap at this point.

0 files changed, 0 insertions, 0 deletions