allow sites to detect flash when shields are down
allow sites to detect flash when shields are down

fix https://github.com/brave/browser-laptop/issues/7549

Auditors: @bridiver

Test Plan:
0. enable flash in preferences
1. go to http://tv-trwam.pl/na-zywo
2. turn off shields. the flash placeholder should appear.

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