Implement CACert queries in SecurityController

Queries are run (on a AsyncTask) when user is switched and when
ACTION_TRUST_STORE_CHANGED is broadcasted. Otherwise, the result is cached
in the SecurityController.

Bug: 37535489
Test: runtest --path frameworks/base/packages/SystemUI/tests/src/com/android/systemui/statusbar/policy/SecurityControllerTest.java

Change-Id: I3b9cc3d85c9f49d0a892613b63d1fba184ab647e

keystore/java/android/security/KeyChain.java

@@ -599,9 +599,9 @@ public final class KeyChain {
         private final Context context;
         private final ServiceConnection serviceConnection;
         private final IKeyChainService service;
-        private KeyChainConnection(Context context,
-                                   ServiceConnection serviceConnection,
-                                   IKeyChainService service) {
+        protected KeyChainConnection(Context context,
+                                     ServiceConnection serviceConnection,
+                                     IKeyChainService service) {
             this.context = context;
             this.serviceConnection = serviceConnection;
             this.service = service;