Revert "Turn off clean-css' advanced optimizations."
Revert "Turn off clean-css' advanced optimizations."

BS3 commits: e31c2edf885efd42d2e755f189cc15125d977d70

2947721120/googlebt4,2947721120/todc-bootstrap,todc/todc-bootstrap,todc/todc-bootstrap,aaroncnhk/todc-bootstrap,ztx1491/todc-bootstrap,mozillo/todc-bootstrap,todc/todc-bootstrap,up2vs/todc-bootstrap