Android 7.0 现象： Windows：
adb shell dumpsys activity activities | findstr mFocusedActivity
Linux:
adb shell dumpsys activity activities | grep mFocusedActivity
Android 8.0
改用：
Windows：
adb shell dumpsys activity activities | findstr mResumedActivity
Linux:
adb shell dumpsys activity activities | grep mResumedActivity
