* Normally the height of scroll indicator is changed dynamically according to the length of scroll content.
* However, when the height policy of scroll indicator is set to be fixed, the height will keep fixed
* regardless of the length of scroll content.
* Normally the height of scroll indicator is changed dynamically according to the length of scroll content.
* However, when the height policy of scroll indicator is set to be fixed, the height will keep fixed
* regardless of the length of scroll content.