GitLab

Adjust Tab search dark mode colors to meet WCAG requirements.
- Selection/Hover colors now match Omnibox colors.
- Fix non-existent variable name

Screenshots:
Before: https://drive.google.com/file/d/1BMIahHv0hNaxuXuAtk228QgGPip9HKJR/view?usp=sharing
After: https://drive.google.com/file/d/16fnTW0bLdwRDp2_VCe3IzuOTsOniGL2k/view?usp=sharing

Bug: 1110109
Change-Id: I087c49a9b98da70ab59f2e433f1487ec1ac008d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2533674Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Commit-Queue: Roman Arora <romanarora@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827277}