code: function _sanitizeStyle(value) {
      value = String(value).trim(); // Make sure it's actually a string.
      if (!value)
          return '';
      // Single url(...) values are supported, but only for URLs that sanitize cleanly. See above for
      // reasoning behind this.
      var urlMatch = value.match(URL_RE);
      if ((urlMatch && _sanitizeUrl(urlMatch[1]) === urlMatch[1]) ||
          value.match(SAFE_STYLE_VALUE) && hasBalancedQuotes(value)) {
          return value; // Safe style values.
      }
      if (isDevMode()) {
          console.warn("WARNING: sanitizing unsafe style value " + value + " (see http://g.co/ng/security#xss).");
      }
      return 'unsafe';
  }
docs: Sanitizes the given untrusted CSS style property value (i.e. not an entire object, just a single
  value) and returns a value that is safe to use in a browser environment.