Revert unnecessary code change
Fix UA stylesheet: remove Rust string escaping
auto merge of #1020 : SimonSapin/servo/external-UA-css, r=jdm

Oops, I broke the UA stylesheet in #1017. The fact that our tests still passed is not a good sign :/
auto merge of #1012 : deokjinkim/servo/glyph_advance_cache, r=ILyoan

#1008 has unnecessary code change. So I want to revert this code.