FreezeBar
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Implements a UI for changing the number of frozen columns on a FlexGrid.

The sample defines a function called 'addFreezeBar' that adds a div element
to a FlexGrid controls and monitors the mouse events to allow users to 
drag this element within the grid.

The 'freezeBar' element snaps to the grid columns as it is dragged, and when
the user releases the mouse, it changes the number of frozen columns on the
grid.