CASE 1, original layer tree
{
  "layers": [
    {
      "name": "Scrolling background of LayoutView #document",
      "bounds": [800, 600],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='composited box behind'",
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#0000FF",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box middle'",
      "bounds": [150, 150]
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    }
  ]
}

CASE 2, hovering over the outer div
{
  "layers": [
    {
      "name": "Scrolling background of LayoutView #document",
      "bounds": [800, 600],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='composited box behind'",
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#0000FF",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box middle'",
      "bounds": [150, 150],
      "invalidations": [
        [0, 0, 141, 141]
      ]
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    }
  ]
}

CASE 3, hovering over the inner div
{
  "layers": [
    {
      "name": "Scrolling background of LayoutView #document",
      "bounds": [800, 600],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='composited box behind'",
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#0000FF",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box middle'",
      "bounds": [150, 150],
      "invalidations": [
        [0, 0, 141, 141]
      ]
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    }
  ]
}