Some properties of KeyboardEvent JS object are not set for Dead keys

See https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent

Try the attached keyboardevent.html to reproduce.

The following properties are unset:

• KeyboardEvent.key must be "Dead"
• KeyboardEvent.keyCode is 0 because of unset content::NativeWebKeyboardEvent::windows_key_code
• KeyboardEvent.which is also 0 because of KeyboardEvent.keyCode