AccumulatedVisualContext Tree:
  [0] transform=[1,0,0,1,0,0] origin=(0,0) (ViewportPaintable(Viewport<#document>))
    [1] scroll_frame_id=1 (ImagePaintable(ImageBox<IMG>))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x40]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x40]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 40x40]
  Save@1
    AddClipRect@1 rect=[0,0 40x40]
    DrawScaledDecodedImageFrame@1 dst_rect=[0,-20 40x80]
  Restore@1
Restore@0