Add ability to show/hide default_home preference.

This adds a new boolean flag, config_show_default_home, which when set
to false will hide the default_home preference item.

Bug: 62378256
Test: make RunSettingsRoboTests
ROBOTEST_FILTER=DefaultHomePreferenceControllerTest

Change-Id: Ibbf17ebb76b61fc8b2eac84016e3d874ca15a513

src/com/android/settings/applications/defaultapps/DefaultHomePreferenceController.java

@@ -24,6 +24,7 @@ import android.content.pm.ActivityInfo;
 import android.content.pm.PackageManager;
 import android.content.pm.ResolveInfo;
 
+import com.android.settings.R;
 import com.android.settingslib.wrapper.PackageManagerWrapper;
 
 import java.util.ArrayList;
@@ -53,7 +54,7 @@ public class DefaultHomePreferenceController extends DefaultAppPreferenceControl
 
     @Override
     public boolean isAvailable() {
-        return true;
+        return mContext.getResources().getBoolean(R.bool.config_show_default_home);
     }
 
     @Override