Don't add any trust agents if the controller is not available.

TrustAgentListPreferenceController gets a list of trust agents and add
them to the security_category preference category at runtime. However,
this update process is always ran - even if the controller is explicitly
disabled/not available. This fixes this.

Bug: None
Test: Updated TrustAgentListPreferenceControllerTest.
Change-Id: Ic95d219bc1d0c7cfa0c4eed0d3dd12dec0e14df6

src/com/android/settings/security/trustagent/TrustAgentListPreferenceController.java

@@ -146,6 +146,10 @@ public class TrustAgentListPreferenceController extends AbstractPreferenceContro
                 mSecurityCategory.removePreference(oldAgent);
             }
         }
+        // If for some reason the preference is no longer available, don't proceed to add.
+        if (!isAvailable()) {
+            return;
+        }
         // Then add new ones.
         final boolean hasSecurity = mLockPatternUtils.isSecure(MY_USER_ID);
         final List<TrustAgentManager.TrustAgentComponentInfo> agents =

tests/robotests/src/com/android/settings/security/trustagent/TrustAgentListPreferenceControllerTest.java

@@ -25,6 +25,7 @@ import static com.google.common.truth.Truth.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -141,4 +142,24 @@ public class TrustAgentListPreferenceControllerTest {
 
         verify(mCategory, atLeastOnce()).addPreference(any(Preference.class));
     }
+
+    @Test
+    @Config(qualifiers = "mcc999")
+    public void onResume_ifNotAvailable_shouldNotAddNewAgents() {
+        final List<TrustAgentManager.TrustAgentComponentInfo> agents = new ArrayList<>();
+        final TrustAgentManager.TrustAgentComponentInfo agent = mock(
+                TrustAgentManager.TrustAgentComponentInfo.class);
+        agent.title = "Test_title";
+        agent.summary = "test summary";
+        agent.componentName = new ComponentName("pkg", "agent");
+        agent.admin = null;
+        agents.add(agent);
+        when(mTrustAgentManager.getActiveTrustAgents(mActivity, mLockPatternUtils))
+                .thenReturn(agents);
+
+        mController.displayPreference(mScreen);
+        mController.onResume();
+
+        verify(mCategory, never()).addPreference(any(Preference.class));
+    }
 }