GitLab

Read system setting and set preferred_color_scheme. Refactor code a bit
to mirror password_echo_enabled. Same as password_echo_enabled, check
system changes when fragment becomes foreground.

Bug: 1070701
Change-Id: Iafcbf6886f8d2f1be474d87759d546182be1562f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153829Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760520}