Layer tree when the fixed elements are out-of-view (should have just a root layer):
{
  "layers": [
    {
      "name": "Scrolling Contents Layer",
      "bounds": [785, 4016],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed1'",
      "bounds": [10, 10],
      "contentsOpaque": true,
      "backgroundColor": "#C0C0C0",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed2'",
      "contentsOpaque": true,
      "drawsContent": false,
      "transform": 2
    },
    {
      "name": "ContentsLayer for Vertical Scrollbar Layer",
      "position": [785, 0],
      "bounds": [15, 600],
      "contentsOpaque": true
    }
  ],
  "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],
        [100, 100, 0, 1]
      ]
    }
  ]
}

Layer tree when the fixed elements are in-view (both fixed elements should have layers):
{
  "layers": [
    {
      "name": "Scrolling Contents Layer",
      "bounds": [785, 4016],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed1'",
      "bounds": [10, 10],
      "contentsOpaque": true,
      "backgroundColor": "#C0C0C0",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed2'",
      "bounds": [10, 10],
      "contentsOpaque": true,
      "backgroundColor": "#C0C0C0",
      "transform": 2
    },
    {
      "name": "ContentsLayer for Vertical Scrollbar Layer",
      "position": [785, 0],
      "bounds": [15, 600],
      "contentsOpaque": true
    }
  ],
  "transforms": [
    {
      "id": 1,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 50, 0, 1]
      ]
    },
    {
      "id": 2,
      "transform": [
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [100, 100, 0, 1]
      ]
    }
  ]
}

Layer tree when the fixed elements are out-of-view again (should have just a root layer):
{
  "layers": [
    {
      "name": "Scrolling Contents Layer",
      "bounds": [785, 4016],
      "contentsOpaque": true,
      "backgroundColor": "#FFFFFF"
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed1'",
      "bounds": [10, 10],
      "contentsOpaque": true,
      "backgroundColor": "#C0C0C0",
      "transform": 1
    },
    {
      "name": "LayoutNGBlockFlow (positioned) DIV id='fixed2'",
      "contentsOpaque": true,
      "drawsContent": false,
      "transform": 2
    },
    {
      "name": "ContentsLayer for Vertical Scrollbar Layer",
      "position": [785, 0],
      "bounds": [15, 600],
      "contentsOpaque": true
    }
  ],
  "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],
        [100, 100, 0, 1]
      ]
    }
  ]
}