Add test for renderers using correctly localized blink/content strings

Adds a regression test for issue 510455 "Choose File" button not being
localized.

Bug: 510455, 952893
Test: added to browser_tests
Change-Id: Ibb4d6e65b308820e1389dcb95eb9a392c9efbb50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575865
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654021}