Add data about Sec-CH-Save-Data

[bershanskiy]

Summary

Add data for HTTP Header Sec-CH-Save-Data.

Test results and supporting details

Chrome Platform Status: https://chromestatus.com/feature/5645928215085056
Chrome bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1293443

Related issues

Content PR: mdn/content#22266

[queengooborg]

Can you provide a source for this change?

[bershanskiy]

One way to test this is to open a page which pings back your headers.

Testing steps for Android devices:

1. On your Android device, open settings and find "Data saver", enable it
2. Disable Wi-Fi and enable mobile data
3. Open the browser and go to https://www.whatismybrowser.com/detect/what-http-headers-is-my-browser-sending
4. Observe SAVE-DATA header with value on

Testing steps for Opera:

1. Open Android device, and open Opera settings (not System settings). enable "Data saver"/"Turbo" mode
2. You may use Wi-Fi or mobile data, this does not matter
3. Open the browser and go to https://www.whatismybrowser.com/detect/what-http-headers-is-my-browser-sending
4. Observe SAVE-DATA header with value on

Testing results:
Chrome 108.0.5357.47 - supports
Opera 72.3.3767.68685 - supports
Firefox 107.1.0 - does not support
Brave 1.45.127 (Chromium 107.0.5304.110) - does not support

More info:

Save-Data was pioneered by Chromium as part of Google Chrome's for Android "Data Saver" mode which later became "Lite" mode.[1][2] Save-Data header also migrated into Opera as part of "Opera Turbo" on and Yandex as part of "Turbo" mode on both desktop and mobile.[2] These features also included a proxy which would compress the data, and reduce image quality. I could not find no reference to Firefox ever implementing this header.

Please note that Chrome 100 had removed the "Lite" mode and associated UI,[3] but the Save-Data header survived and is now based on Android Data Saver API.[4] This is just a simple preference now, without any proxies in Chrome. Opera still retained the UI and proxy functionality.

[1] https://css-tricks.com/help-users-save-data/
[2] https://web.dev/optimizing-content-efficiency-save-data
[3] https://support.google.com/chrome/thread/151853370
[4] https://chromium-review.googlesource.com/c/chromium/src/+/3573287