getClientRects 方法
实现
List<Rectangle> getClientRects() {
var value = _getClientRects();
// If no prototype we need one for the world to hookup to the proper Dart class.
var jsProto = JS('', '#.prototype', value);
if (jsProto == null) {
JS('', '#.prototype = Object.create(null)', value);
}
applyExtension('DOMRectList', value);
return value;
}