Use defaultValue, remove setter
Use defaultValue, remove setter

likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium