如果SYSTEM_ALERT_WINDOW權限可用，則返回true。
*從Q開始，在低ram手機上禁用SYSTEM_ALERT_WINDOW。

vendor/mediatek/proprietary/packages/apps/MtkSettings/src/com/android/settings/Utils.java

public static boolean isSystemAlertWindowEnabled(Context context) {
? ? ? ? // SYSTEM_ALERT_WINDOW is disabled on on low ram devices starting from Q
? ? ? ? ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
? ? ? ? return true/*!(am.isLowRamDevice() && (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q))*/;
? ? }