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=[0,0 800x80]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x80]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 120x80]
  CompositorMainThreadWheelEventRegion@1 rect=[0,0 120x80]
  Save@1
    AddClipRect@1 rect=[0,0 120x80]
    DrawCompositorSurface@1 dst_rect=[0,0 120x80]
  Restore@1
Restore@0
