Remove downloadsBarOffset for new coordinate calculation
Remove downloadsBarOffset for new coordinate calculation

fix #9020

Auditors: @bsclifton, @bbondy

Test Plan:
1. Open about:autofill
2. Create an entry
3. Open www.roboform.com/filling-test-all-fields
4. Download that page
5. Trigger the autofill pulldown with different UI scale

timborden/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop,timborden/browser-laptop,luixxiul/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,timborden/browser-laptop,timborden/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop