WebUI Dark Mode: update NTPResourceCache

This provides $i18n{dark} in certain cases and tracks updates.

R=dpapad@chromium.org
BUG=930269,925384

Change-Id: Ief487aaaaf286ca5f96f5f12e6ece3acc707ffc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1519929
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#640656}
2 files changed