Keyboard handling problem in Webkit based browsers

[allencblee]

When pressing the down arrow key to move to the next row, the focused row jumps to the middle of the grid when attempting to scroll up the grid. This happens in webkit browsers only. The strange bouncing behaviour happens when using the up arrow key to scroll down the grid. This is related to #1043 but the latest fix doesn't resolve the problem completely.

[kfranqueiro]

I noticed this and this was actually part of the reason I debounced when fixing that issue (aside from performance) - I wanted to leave browsers' default behavior intact in that regard. I'll ask the team for more input on what they think about the difference in behavior, though I'm not sure what to do to resolve it that wouldn't amount to removing the debounce and affecting performance instead.

[allencblee]

@kfranqueiro Thanks for prompt response. IMHO, there shouldn't be performance problems even if there's no debouncing because the keyboard typematic rate is only 11 keys/sec. On the contrary, after adding the debouncing, the bouncing effect gives users an impression that the scrolling is not fast enough to be smooth.