Reverting the kDisableWindows10CustomTitlebar switch removal

[logoffon]

The recent removal of --disable-windows10-custom-titlebar switch meant that Chromium and its derivatives can no longer have consistent appearance for users with visual style/theme customization (such as AeroGlass, WindowBlinds, MicaForEveryone, etc.). There is simply no reason to draw a custom title bar when the native one can do just fine, and conforms to whatever the theme the user is set.

[teknixstuff]

I'd like this reverted too!

[teknixstuff]

@logoffon you might need to send this to the chromium mailing list, since github is just a mirror of the source and not where actual work happens.

[7kt4]

I also highly suggest to add this back, there is a very significant number of people who use third-party themes on Windows