Revert "Remove unused SharedURLLoaderFactory getter from client"

This reverts commit 4fbe638c763b01d2c24c874ed70b6627d6b214e4.

Reason for revert: Relanding

Original change's description:
> Remove unused SharedURLLoaderFactory getter from client
>
> Bug: b:349891147
> Change-Id: I6a6a2100e6f4992b5638aa495461cf977689f4d4
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5670226
> Commit-Queue: Michael Cui <mlcui@google.com>
> Auto-Submit: Michael Cui <mlcui@google.com>
> Reviewed-by: Darren Shen <shend@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1324063}

Bug: b:349891147
Change-Id: I0a1f6378fe8da95e31087ea9b054a4683fb560ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5881582
Commit-Queue: Darren Shen <shend@chromium.org>
Reviewed-by: Michael Cui <mlcui@google.com>
Cr-Commit-Position: refs/heads/main@{#1364746}