Test overlap is rendered correctly when hovering over elements

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'",
      "position": [180, 180],
      "bounds": [140, 140],
      "backgroundColor": "#00FFFF"
    }
  ],
  "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 "middle" element (causes that div to become its own composited layer)
{
  "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": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#008000",
      "transform": 2
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box middle2'",
      "position": [200, 200],
      "bounds": [120, 120],
      "backgroundColor": "#00FFFF"
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    },
    {
      "id": 2,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [180, 180, 0, 1]
      ]
    }
  ]
}

Case 3: hovering over the "middle2" element (causes that div to become its own composited layer)
{
  "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'",
      "position": [180, 180],
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#00FF00"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box middle2'",
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#008000",
      "transform": 2
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box top'",
      "position": [220, 220],
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#00FFFF"
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    },
    {
      "id": 2,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [200, 200, 0, 1]
      ]
    }
  ]
}

Case 4: hovering over the "top" element (causes that div to become its own composited layer)
{
  "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'",
      "position": [180, 180],
      "bounds": [120, 120],
      "backgroundColor": "#FF00FF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV class='box top'",
      "bounds": [100, 100],
      "contentsOpaque": true,
      "backgroundColor": "#008000",
      "transform": 2
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    },
    {
      "id": 2,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [220, 220, 0, 1]
      ]
    }
  ]
}

Case 5: back to situation in case 1
{
  "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'",
      "position": [180, 180],
      "bounds": [140, 140],
      "backgroundColor": "#00FFFF"
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    }
  ]
}