Remove native KeyEvent

Relying on any native implementation of window.KeyEvent is
unreliable. The two specs listed in the comments for this method
are not the same and Firefox now has DOM_VK_ENTER and
DOM_VK_RETURN which are equivalent to 13 and 14 respectively.
The key on the right side of my home row triggers 14 using
native window.KeyEvent in Firefox, where Chrome uses our
defined constants and returns 13. This fix ensures the same
values for all browsers.

Change-Id: I12b2f5d674bdf13526577cb81d0505b608f2846c
Merge "Remove native KeyEvent"