AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))
    [6] clip=[8,108 100x100] (PaintableWithLines(BlockContainer<DIV>.child))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x221]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x200]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,108 100x100]
  CompositorWheelHitTestTarget@6 target_scroll_frame_index=0 rect=[8,108 50x50]
  FillRect@6 rect=[8,108 50x50] color=rgb(255, 0, 0)
Restore@0