Three main changes:
1. Use the pixel metrics of the style instead of hardcoded values.
2. Account for the potential sort indicator in the column header.
3. In the two "Size" columns, the largest numerical value does not
   necessarily result in the widest text string, so just use the
   value 8888.88 to estimate the width (we assume that 8 is the
   widest digit, which is true for many proportional fonts).