Refactored TrustAgentUtils to allow agent check injection.

Notes:
- TrustAgentUtils defined a method that allowed callers to determine if a Trust Agent package is allowed to provide trust. If it is, it adds it to the list of available trust agents that can be displayed in the Settings->Security screen.
- The logic used to define what agents are permitted on the device can now be injected.

Test: Ran 'm RunSettingsRoboTest' and added a new test for the TrustAgentFeatureProviderImpl.
Bug: 34354635
Change-Id: I24c54c14bde26073ce6fa907379b86aae2841600

src/com/android/settings/security/SecurityFeatureProviderImpl.java

@@ -22,6 +22,8 @@ import android.content.IContentProvider;
 import android.content.pm.PackageManager;
 import android.content.res.Resources;
 import android.graphics.drawable.Drawable;
+import com.android.settings.trustagent.TrustAgentManager;
+import com.android.settings.trustagent.TrustAgentManagerImpl;
 import com.android.settingslib.drawer.DashboardCategory;
 import android.support.v4.content.ContextCompat;
 import android.support.v7.preference.Preference;
@@ -37,6 +39,8 @@ import java.util.Map;
 /** Implementation for {@code SecurityFeatureProvider}. */
 public class SecurityFeatureProviderImpl implements SecurityFeatureProvider {
 
+    private TrustAgentManager mTrustAgentManager;
+
     /** Update preferences with data from associated tiles. */
     public void updatePreferences(Context context, PreferenceScreen preferenceScreen,
             DashboardCategory dashboardCategory) {
@@ -114,4 +118,12 @@ public class SecurityFeatureProviderImpl implements SecurityFeatureProvider {
             }
         }
     }
+
+    @Override
+    public TrustAgentManager getTrustAgentManager() {
+        if (mTrustAgentManager == null) {
+            mTrustAgentManager = new TrustAgentManagerImpl();
+        }
+        return mTrustAgentManager;
+    }
 }