Improve switch comments for --site-per-process and --process-per-site
Improve switch comments for --site-per-process and --process-per-site

BUG=None

Review URL: https://codereview.chromium.org/1693163002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#375614}

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