Based on UI designer folks requirement, change the default font size in ChromeOS from 12px to 13px.
Based on UI designer folks requirement, change the default font size in ChromeOS from 12px to 13px.

BUG=449675
TEST=zha@, sgabriel@ manually checked on devices (1x, 2x)

Review URL: https://codereview.chromium.org/887153002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#314363}

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