在 ActionBar顯示進度圖示

Reference:

http://androidbiancheng.blogspot.tw/2011/07/windowfeatureindeterminateprogress.html

步驟：

1. requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
2. 呼叫 setProgressBarIndeterminateVisibility(true/false) 方法來顯示/隱藏進度圖示