Turn a11y paint CHECKs into DCHECKs

The logs for RunAccessibilityPaintChecks previously looked like CHECKs,
which is confusing as they are only enabled in debug builds. This has
gotten them incorrectly labeled as Pri-0 CHECK() crashes.

Bug: 1218186, 1275928
Change-Id: I5d2b547d17bc4cd9b9f1bbeba31de615a17000a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3312747
Auto-Submit: Peter Boström <pbos@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#948085}