Before:
AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x93]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x72]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 100x72]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 69.625x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,26 47.0625x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,44 60x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,62 36.46875x18]
  DrawGlyphRun@1 rect=[8,8 70x18] translation=[8,21.796875] color=rgb(0, 0, 255)
  DrawLine@1 from=[8,25] to=[78,25] color=rgb(0, 0, 255) thickness=2
  DrawGlyphRun@1 rect=[8,26 48x18] translation=[8,39.796875] color=rgb(0, 0, 255)
  DrawLine@1 from=[8,43] to=[55,43] color=rgb(0, 0, 255) thickness=2
  DrawGlyphRun@1 rect=[8,44 60x18] translation=[8,57.796875] color=rgb(0, 0, 255)
  DrawLine@1 from=[8,61] to=[68,61] color=rgb(0, 0, 255) thickness=2
  DrawGlyphRun@1 rect=[8,62 37x18] translation=[8,75.796875] color=rgb(0, 0, 255)
  DrawLine@1 from=[8,79] to=[44,79] color=rgb(0, 0, 255) thickness=2
Restore@0

After:
AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x93]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x72]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 100x72]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 69.625x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,26 47.0625x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,44 60x18]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,62 36.46875x18]
  DrawGlyphRun@1 rect=[8,8 70x18] translation=[8,21.796875] color=rgb(255, 0, 0)
  DrawLine@1 from=[8,25] to=[78,25] color=rgb(255, 0, 0) thickness=2
  DrawGlyphRun@1 rect=[8,26 48x18] translation=[8,39.796875] color=rgb(255, 0, 0)
  DrawLine@1 from=[8,43] to=[55,43] color=rgb(255, 0, 0) thickness=2
  DrawGlyphRun@1 rect=[8,44 60x18] translation=[8,57.796875] color=rgb(255, 0, 0)
  DrawLine@1 from=[8,61] to=[68,61] color=rgb(255, 0, 0) thickness=2
  DrawGlyphRun@1 rect=[8,62 37x18] translation=[8,75.796875] color=rgb(255, 0, 0)
  DrawLine@1 from=[8,79] to=[44,79] color=rgb(255, 0, 0) thickness=2
Restore@0