Fix mobility inference in ChromeDriver

Inferrence of clientHints.mobile from deviceMetrics.mobile is incorrect
because usually tablets have deviceMetrics.mobile=true, meaning that
the user agent must behave a mobile user agent, while their
clientHints.mobile must be false. i.e. use the desktop site version.
With this commit clientHints.mobile is inferred from userAgent on
Android and as false on other platforms.

Bug: chromedriver:4243
Change-Id: Iebd95aadce26b2fe71746ec562440f1ce774763a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4649348
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Vladimir Nechaev <nechaev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1162869}