Making layer decision at frame tree means to decide the layer a frame painted on according the information of frame tree. For now, we create painted layer after process display item, we don't know what layer a frame will be painted on during building display list. If we know the layer, we could maintain dirty regions at frame tree too, so the less items will be built too.
https://public.etherpad-mozilla.org/p/move_layer_decesion_to_frame_tree The basic idea of how to do it.
You need to log in before you can comment on or make changes to this bug.