Processes postback data for the System.Web.UI.WebControls.DropDownList control.
true if the System.Web.UI.WebControls.DropDownList control's state changes as a result of the postback event; otherwise, false.
The ASP.NET page framework tracks all the server controls that return true from this method call, and then invokes the DropDownList.RaisePostDataChangedEvent method on the System.Web.UI.WebControls.DropDownList control.