LibWeb: Leaving a tab idling for 30+ minutes leads to a blank page (bar some glitches) and allocation failures in the log

[MacDue]

I left Ladybird idling on https://github.com/SerenityOS/serenity (but I've noticed the same issue occur on other sites), came back after a stroll, and the page was blank (bar some glitches), with the log full of bitmap allocation failures (of progressively larger sizes):

5301.381 WebContent(14937): Unable to allocate temporary bitmap [0,12864 184128x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
5302.137 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6240.320 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6240.916 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6241.596 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6242.252 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6248.097 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow
6254.165 WebContent(14937): Unable to allocate temporary bitmap [0,12864 244224x4608] for box-shadow rendering: Gfx::Bitmap backing store size overflow

A few stray pixels in the top left corner (of the otherwise blank page):