Before clip change:
AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))
    [2] clip=[8,13 100x100] (PaintableWithLines(BlockContainer<DIV>#box.box))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x21]
  CompositorWheelHitTestTarget@2 target_scroll_frame_index=0 rect=[8,13 100x100]
  FillRect@2 rect=[8,13 100x100] color=rgb(173, 216, 230)
  DrawGlyphRun@2 rect=[8,13 30x18] translation=[8,26.796875] color=rgb(0, 0, 0)
Restore@0

After clip change:
AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))
    [2] clip=[18,23 80x80] (PaintableWithLines(BlockContainer<DIV>#box.box))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x21]
  CompositorWheelHitTestTarget@2 target_scroll_frame_index=0 rect=[8,13 100x100]
  FillRect@2 rect=[8,13 100x100] color=rgb(173, 216, 230)
  DrawGlyphRun@2 rect=[8,13 30x18] translation=[8,26.796875] color=rgb(0, 0, 0)
Restore@0