When no chrome_binary is configured, auto-detect Chrome for Testing
at ~/.chrome-for-testing/ and use it instead of letting ChromeDriver
fall back to system Chrome. This prevents the frequent version
mismatch error caused by system Chrome auto-updating independently
of the ChromeDriver installed by setup-chrome-for-testing.sh.
Checks mac-arm64, mac-x64, and linux64 paths. Falls back to system
Chrome (previous behavior) if Chrome for Testing is not installed.
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