function $BrowserProvider(){
  this.$get = ['$window', '$log', '$sniffer', '$document',
      function( $window,   $log,   $sniffer,   $document){
        return new Browser($window, $document, $document.find('body'), $log, $sniffer);
      }];
}
Returns current <base href>
(always relative - without domain)

@returns {string=}