WebUI Dark Mode: make chrome://apps actually use NTP_COLOR_LINK from theme

Screenshots: https://imgur.com/a/r9Zhvy7

R=dpapad@chromium.org
BUG=925384

Change-Id: Ide9c75d69c9cace5b7d1b50963b4711bac86b7fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1533179
Auto-Submit: Dan Beam <dbeam@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643251}
3 files changed