Default theme should be dark or light depending on Windows 10 preference

[btlechowski]

Follow up to #1189

This feature has been implemented on MacOS, but Windows version had some problems and is hidden behind a flag. brave/brave-core#1805 (review)

Steps to Reproduce

1. Clean install
2. Launch Browser
3. Check theme settings have three options (Same as Windows, Dark, Light)
4. Check Same as Windows applies Windows theme to brave theme
5. Check Dark/Light works independently with Windows theme.

Actual result:

There is no Same as Windows in Brave colors

Expected result:

Same as Windows is available in Brave colors
Same as Windows is the default option on Windows 10

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave	0.62.32 Chromium: 73.0.3683.75 (Official Build) beta (64-bit)
Revision	909ee014fcea6828f9a610e6716145bc0b3ebf4a-refs/branch-heads/3683@{#803}
OS	Windows 10 OS Build 17134.523

Brave	0.63.14 Chromium: 73.0.3683.75 (Official Build) dev (64-bit)
Revision	909ee014fcea6828f9a610e6716145bc0b3ebf4a-refs/branch-heads/3683@{#803}
OS	Windows 10 OS Build 17134.523

cc @brave/legacy_qa @petemill @simonhong

[simonhong]

This is expected behavior for now because upstream disabled dark theme support on Win10.
When they enable it, we can consider this option again.

[srirambv]

@btlechowski have you checked with setting apps colour?

By default the app is set to light always.

[simonhong]

@srirambv @btlechowski We don't need to test theme on Windows for now.
Chromium didn't enable platform theme support on Win10 yet.

[simonhong]

@btlechowski We can test Same as Windows feature since 0.63 (currently beta)

[kjozwiak]

@simonhong was this upstreamed in one of the C74 bumps?

[simonhong]

@kjozwiak beta(C74) has Same as Windows option and it's default.
However, needs more fixes to make theme works properly on Windows like MacOS.
Fix for #4059 is merged and waiting for uplifting.
Fix for #4056 is waiting for review.
When all above fixes are uplifted to C74, brave theme will work properly in Windows.

[btlechowski]

Verification passed on

Brave	0.66.87 Chromium: 75.0.3770.80 (Official Build) beta (64-bit)
Revision	9a9aa15057b6b2cc0909bdcf638c0b65ecd516f2-refs/branch-heads/3770@{#948}
OS	Windows 10 OS Version 1809 (Build 17763.379)

Verified test plan from brave/brave-core#2352 and from the description. Checked changing Same as Windows(Dark)->Same as Windows(Light) and Same as Windows(Light)->Same as Windows(Dark). Checked settings dropdown, permissions alert box (notifications, geolocation, translations, alerts) and downloads bar.