split tools_browsertest into separate files per tool

- This should be a no-op, all test coverage remains the same.

Bug: 432498692
Change-Id: I482a54603eb6d958470498ad8421457e61e08ad2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6765748
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Rodney Ding <rodneyding@google.com>
Cr-Commit-Position: refs/heads/main@{#1489621}