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This enables reusing LoginPasswordView and LoginPinView with
custom colors, e.g. for in-session auth dialog and dark mode
in the future.

Bug: b:156258540
Test: deploy to Nami device, looks the same as without the change.
Change-Id: Ic7ec4be3327fa4a94571543d41ba5030807389b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2333823Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Yicheng Li <yichengli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796470}