Add use-counter and WebDX feature mapping for file-selector-button.
Change-Id: I0e1faf02c931bc5b25f78bc71b2cfa4b872ec44a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6003165
Reviewed-by: Rune Lillesveen futhark@chromium.org
Commit-Queue: Steinar H Gunderson sesse@chromium.org
Reviewed-by: Noam Rosenthal nrosenthal@chromium.org
Cr-Commit-Position: refs/heads/main@{#1380348}