Boundary condition of query results multiple result set display calculation is a few pixels off

[cssuh]

Steps to Reproduce:

1. Run a query with multiple result sets
2. Resize the query result window so that the availableHeight is ~550px
3. Observe the following:
   

Expected:
Properly aligned results grids & query toolbar buttons

Actual:
the top result grid is wider than the bottom result grid, and the query toolbar buttons are partially obscured by the scrollbar (but this is fixed if you make the results grid a few pixels taller or shorter)