Convert StringPiece to std::string_view in //pdf

Bug: 40506050
Change-Id: I6774a26d242aa72e920da8bf505a226c518f412b
Signed-off-by: Md Hasibul Hasan <hasibulhasan873@gmail.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5385507


Commit-Queue: K. Moon <kmoon@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279497}