viz: const-ify DisplayResourceProvider

Minor cleanup to add const to DisplayResourceProvider where possible.
This lets callers of DisplayResourceProvider be const more often.

Change-Id: I0968c48631b4e8a64d0dc12b95587e3e461f6dd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5427574


Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Michael Tang <tangm@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1283198}