🛃 Split out Custom Tabs status bar color code.

This code should have no behavioural change - it's just a small CL to
split the code out and add tests.

Bug: 964914
Change-Id: I0a6d3b356931ddaa7863f490cddc4009195a8495
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621174
Reviewed-by: Pavel Shmakov <pshmakov@chromium.org>
Reviewed-by: Michael van Ouwerkerk <mvanouwerkerk@chromium.org>
Commit-Queue: Peter Conn <peconn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661723}
6 files changed