fix urlbar compatibility with Google IME on OS X
fix urlbar compatibility with Google IME on OS X

IME on OS X seems to only work properly if the ENTER event is detected
on keydown.
fix https://github.com/brave/browser-laptop/issues/5315
fix https://github.com/brave/browser-laptop/issues/5313

Auditors: @luixxiul

Test Plan:
1. install google IME, enable japanese
2. hit a in the urlbar
3. hit enter once. it should decide the candidate.
4. hit enter again. it should search the candidate.

jonathansampson/browser-laptop,jonathansampson/browser-laptop,timborden/browser-laptop,pmkary/braver,dcposch/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,willy-b/browser-laptop,willy-b/browser-laptop,diasdavid/browser-laptop,jonathansampson/browser-laptop,dcposch/browser-laptop,pmkary/braver,pmkary/braver,willy-b/browser-laptop,darkdh/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,dcposch/browser-laptop,dcposch/browser-laptop,diasdavid/browser-laptop,jonathansampson/browser-laptop,pmkary/braver,timborden/browser-laptop,timborden/browser-laptop,timborden/browser-laptop,darkdh/browser-laptop,darkdh/browser-laptop,luixxiul/browser-laptop,darkdh/browser-laptop,willy-b/browser-laptop