Don't optimize future reserved keywords
Don't optimize future reserved keywords

Summary: It breaks Safari. For example, class is a future reserved keyword,
         don't change b['class'] to b.class.

Reviewed By: lklots

Test Plan: test following js file:

           var a = {'class' : 10}
           print(a['class'])

           It should not be changed to
           var a = {'class' : 10} print(a.class)

Revert: OK

DiffCamp Revision: 78052

facebookarchive/libfbjs,facebookarchive/libfbjs