Try both Sans and Arial for last resort fallback font

Arial may be unavailable on some Linux platforms.

BUG=350976
TEST=FontCacheTest.getLastResortFallbackFont

Review URL: https://codereview.chromium.org/189663016

git-svn-id: svn://svn.chromium.org/blink/trunk@168865 bbb929c8-8fbe-4397-9dbb-9b2b20218538