Implement OS Version Detection for the User Agent

[MeFisto94]

User Agent now correctly reports Windows 7, 8.1, 10, ...

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• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #18194
• These changes do not require tests, because that would involve testing servo across all windows versions, to be meaningful

[highfive]

Thanks for the pull request, and welcome! The Servo team is excited to review your changes, and you should hear from @paulrouget (or someone else) soon.

[MeFisto94]

In order to test this changes, surf to "https://www.whatsmyua.info or "https://www.whatismybrowser.com/detect/what-is-my-user-agent (the latter shows another issue: analyseing the UA fails due to some CSRF problem).

I did only test this on Windows 10, but the crate is fairly simple and as such I don't expect any issues, apart from the following two:

• The crate still uses 0.2.8 winapi, which makes test-tidy fail:

./Cargo.lock:1: duplicate versions for package `winapi`
The following packages depend on version 0.2.8 from 'crates.io':
The following packages depend on version 0.3.8 from 'https://github.com/servo/winapi-rs?branch=patch-1':

See stanislav-tkach/os_info#111 for tracking

• The crate doesn't work on UWP, which doesn't really have a concept of a Windows Version either (stanislav-tkach/os_info#112), thus it has just been excluded in this PR.

Also note the usage of Box::leak, maybe you have a different vision. I also removed the const DESKTOP_UA_STRING: &'static str =

[paulrouget]

winapi duplicate versions is annoying. Do we have to use os_info? How does os_info::get().version().version() work?

[MeFisto94]

Someone already created an issue for winapi 0.30 on os_info. We could also submit a PR.
The code itself is really small, though and we probably don't need it for Linux and most of the other supported OS anyway. Only for Mac OS X maybe.

[atouchet]

The latest version of os_info is now using winapi 0.3.

[jdm]

This seems fine to me. Please update to the latest version of os_info and we can merge this.

[jdm]

This statement should not be necessary in the 2018 edition of Rust, which components/config/Cargo.toml enables.

[jdm]

Thinking about this a little harder, and how to avoid the leak and compilation error on non-windows, I'm becoming more hesitant about merging this. It only affects desktop windows builds, and only impacts windows versions that are already end-od-life. I am incluned to stick with the existing implementation and avoid the complexity without a compelling motivation otherwise.

[jdm]

I just noticed that this will leak memory on every network request.

[MeFisto94]

While it doesn't change much about the reasoning, I think or better put assumed that this would happen only once on startup in https://github.com/MeFisto94/servo/blob/a4471368965d30c08042b73b5d475558a2e277f0/components/config/opts.rs#L567

[jdm]

Ah, right. My mistake.