KeyboardEvent.location should be DOM_KEY_LOCATION_STANDARD for Num Lock key

KeyboardEvent.location should be DOM_KEY_LOCATION_STANDARD for Num Lock key.
This behavior is consistent with IE and Firefox. However, Blink returns
DOM_KEY_LOCATION_NUMPAD for it on Windows (the value is correct on Mac and
Linux).

This patch fixes Blink on Windows to be inline with the others.

BUG=263724

Review URL: https://chromiumcodereview.appspot.com/22831043

git-svn-id: svn://svn.chromium.org/blink/trunk@156693 bbb929c8-8fbe-4397-9dbb-9b2b20218538