downgrade: base::StringPiece -> std::string_view

Bug: 691162
Change-Id: Ia8f89a5e57edb5e4d8b58d5f2d54e0effb9d3afa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5377800


Reviewed-by: Greg Thompson <grt@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Helmut Januschka <helmut@januschka.com>
Cr-Commit-Position: refs/heads/main@{#1278873}