scroller scrollTop: 100
window scrollY: 0
display list:
AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))
    [2] clip=[0,0 100x100]
      [3] scroll_frame_id=2 (PaintableWithLines(BlockContainer<DIV>#spacer))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=1 rect=[0,0 800x600]
  CompositorScrollNode@0 scroll_frame_index=1 parent_scroll_frame_index=0 scrollport_rect=[0,0 800x600] max_scroll_offset=[0,1513] is_viewport=true
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=1 rect=[0,0 800x2113]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=1 rect=[0,0 800x2100]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=2 rect=[0,0 100x100]
  CompositorScrollNode@1 scroll_frame_index=2 parent_scroll_frame_index=1 scrollport_rect=[0,0 100x100] max_scroll_offset=[0,400] is_viewport=false
  CompositorWheelHitTestTarget@3 target_scroll_frame_index=2 rect=[0,0 100x500]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=1 rect=[0,100 800x2000]
  PaintScrollBar@1
Restore@0