Spoof Android Desktop User Agent as ChromeOS instead of Linux

Adds the `kAndroidDesktopUASpoofAsChromeOS` feature to report Android
devices as ChromeOS instead of Linux.

Details in go/white-lie-to-fix-another-white-lie

Bug: 507566377
Change-Id: I8ea53c89ec9fa59bbacf015d54b8d113564f96f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7802707
Reviewed-by: Mike Taylor <miketaylr@chromium.org>
Commit-Queue: Mike Taylor <miketaylr@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Sangwhan Moon <sxm@google.com>
Cr-Commit-Position: refs/heads/main@{#1627820}
NOKEYCHECK=True
GitOrigin-RevId: 8dedf95dcbffc76fe60d07ad345c0e0d0c16b907