title: Conditionally set grid column width
body: <p>I have a Grid with two columns. I want the leftmost column's width to be either 50% of the available width of the Grid, or the width required to fit any controls contained within the column, whichever is greater. How can I achieve this?</p>
  
  <p>Put differently, I want the column to take up as little width as possible, but with a minimum of 50%.</p>