偶然发现，如果将两个scrollview放到一个vertical layout里面，第一个scrollview的高度会奇怪的被压了几个像素，导致垂直滚动条露了出来。
测试代码：
private Vector2 scrollPos;
private Vector2 scrollPos2;
void OnGUI()
{
scrollPos = GUILayout.BeginScrollView(scrollPos, "scrollview"/*, GUILayout.ExpandHeight(false), GUILayout.ExpandWidth(false)*/);
GUILayout.Box("", "box", GUILayout.Height(50), GUILayout.Width(1000));
GUILayout.EndScrollView();
scrollPos2 = GUILayout.BeginScrollView(scrollPos2, "scrollview"/*, GUILayout.ExpandHeight(false), GUILayout.ExpandWidth(false)*/);
GUILayout.Box("", "box", GUILayout.Height(1000), GUILayout.Width(50));
GUILayout.EndScrollView();
}
