Set device credential's Window flag to be SECURE.

This prevents showing any pattern/pin in recent list.

Change-Id: Ie56f725bf245961d61a66eae8a82b728600cb650
Fixes: 64339515
Bug: 38258991
Merged-In: Ife33131004d66092bfa57aa57a9bb856800ce28d
Merged-In: Ia9935ef710cf1795d9ce464e0a9edff75be9c0c3
Merged-In: I99c283dd4a1f2d579f565ccf5839a705e75ed6fc
Merged-In: Ibe781a3a1e1483a8c6fde4c7cc5dffbf54bdba59
Test: manual
diff --git a/src/com/android/settings/ConfirmDeviceCredentialBaseActivity.java b/src/com/android/settings/ConfirmDeviceCredentialBaseActivity.java
index 176efbc..3da1766 100644
--- a/src/com/android/settings/ConfirmDeviceCredentialBaseActivity.java
+++ b/src/com/android/settings/ConfirmDeviceCredentialBaseActivity.java
@@ -36,6 +36,7 @@
             mDark = true;
         }
         super.onCreate(savedState);
+        getWindow().addFlags(WindowManager.LayoutParams.FLAG_SECURE);
         boolean deviceLocked = getSystemService(KeyguardManager.class).isKeyguardLocked();
         if (deviceLocked && getIntent().getBooleanExtra(
                 ConfirmDeviceCredentialBaseFragment.SHOW_WHEN_LOCKED, false)) {