function unionArrays(arrs) {
      var map = {};
      for (var i = arrs.length; --i >= 0;) {
        var arr = arrs[i];
        for (var j = arr.length; --j >= 0;) {
          map[arr[j]] = ALLOWED_LITERAL;
        }
      }
      return map;
    }
Given a series of normalized CSS tokens, applies a property schema, as
defined in CssPropertyPatterns.java, and sanitizes the tokens in place.
@param property a property name.
@param tokens as parsed by lexCss.  Modified in place.
@param opt_naiveUriRewriter a URI rewriter; an object with a "rewrite"
    function that takes a URL and returns a safe URL.
@param opt_baseURI a URI against which all relative URLs in tokens will
    be resolved.
@param opt_idSuffix {string} appended to all IDs to scope them.