third part apps can disable the secret lockscreen

[Preconditions]
set password or patten lockscreen

[operating steps]
1.install the app (eg QQBrowser) and connected wifi
2.wait a while,the weather notification will shown on statusbar
3.turn off screen,the weather notification will shown on lockscreen too.
4.click the search bar in weather notification,it will disable lockscreen.
5.press HOME button or kill QQBrowser in Recent apps,you can operate the phone

packages/SystemUI/src/com/android/systemui/keyguard/KeyguardViewMediator.java

@@ -773,6 +773,11 @@ public class KeyguardViewMediator extends SystemUI {
         synchronized (this) {
             if (DEBUG) Log.d(TAG, "setKeyguardEnabled(" + enabled + ")");
 
+            if (isSecure()) {
+                Log.d(TAG, "current mode is SecurityMode, ignore hide keyguard");
+                return;
+            }
+
             mExternallyEnabled = enabled;
 
             if (!enabled && mShowing) {