forming a monotonically increasing sequence (e.g. with position:sticky)
Relative positioning can cause table parts to move, which can cause
issues with the cursor position to know which rows can be skipped.
To make this work, use the max difference between the frame's rect and
the union of the frame's "normal" position and the overflow rect to
cover the area of relatively positioned elements even if they are out of
order.
This resolves#1309.
list items.
This patch does the following things:
1. Creates nsDisplayTableBorderCollapse that draws all collapse border
of tables.
2. Stops the use of nsDisplayTableBorderBackground.
3. Lets column and column group frames generate display items.
4. When traversing the table, also traverses the column and column group
frames.
5. For each type of table frame (col group, col, row group, row and
cell), draws their own background.
