Update new spec for ThemePicker preview

New spec: https://screenshot.googleplex.com/FqnN1azFvCy.png
Screenshot:
    Normal https://screenshot.googleplex.com/uJNijGGH8c5.png
    Largest font and display size https://screenshot.googleplex.com/p80aYxjYMoO.png

Test: Manually
Bug: 157402935
Change-Id: I5b9c3ddee215e83e925b5b332934f1596d247a92
3 files changed