@TargetApi(Build.VERSION_CODES.M)
    protected StatusBarNotification[] getActiveNotifications() {
        ensureOnCreateCalled();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            return mNotificationManager.getActiveNotifications();
        }
        throw new IllegalStateException("getActiveNotifications cannot be called pre-M.");
    }
Returns a list of active notifications, essentially calling
NotificationManager#getActiveNotifications. The default implementation does not work on
pre-Android M.
@return An array of StatusBarNotification.
customtabs/src/android/support/customtabs/trusted/TrustedWebActivityService.java