This tests viewport datagrid.
Nodes attached to dom:
a0
a1
a2
a3
a4
a5
a6

Scrolled down to 133px
Nodes attached to dom:
a6
a7
a8
a9
a10
a11
a12

Scrolled down to 312px
Nodes attached to dom:
a15
a16
a17
a18
a19
a20
a21

Scrolled down to 1000px - should be at bottom
Nodes attached to dom:
a23
a24
a25
a26
a27
a28
a29

Scrolled up to 0px
Nodes attached to dom:
a0
a1
a2
a3
a4
a5
a6

Testing removal of some nodes in viewport
Should be missing node 0, 1, 3, 5 from dom:
Nodes attached to dom:
a2
a4
a6
a7
a8
a9
a10

Testing adding of some nodes back into viewport
Nodes should be the same as previous dump because of throttling:
Nodes attached to dom:
a2
a4
a6
a7
a8
a9
a10

Should have nodes 0, 1, 3, 5 back in dom and previously added nodes removed:
Nodes attached to dom:
a0
a1
a2
a3
a4
a5
a6