I think this pull request should get merged then Randy can refactor them in to string utils and reuse them in #4885. We should probably just expose a single export from CSSUtils (not StringUtils) for this to reducing the content for CSS parsers because it doesn't work for JavaScript or other languages.  CSS doesn't have the // comment syntax whereas JS does.  

Perhaps the exported name should be something like reduceStyleSheetForRegExParsing() because it removes strings as well as comments.  It's generally not a good idea to remove strings but we want to avoid parsing matches in quoted strings so that's why it's here.