fix(demo): Listen to "keydown" on settings button.
fix(demo): Listen to "keydown" on settings button.

Previously, in the demo, we were only listening to "click" events
on the button that opens the settings menu.
Normal button elements produce "click" events when activated via
keyboard navigation. However, it turns out that the MDL drawer
button element is actually a div with the ARIA role of a button,
and thus it is only producing a "keydown" event in that case.
So this makes us also listen for "keydown" events.

Fixes #2986

Change-Id: I4142fb20125107c858d5b8b33c6e9c4657adf715

tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player