Declare "searchable" attribute for preferences.

Now we can easily mark a preference nonIndexable in xml instead of
adding key into searchIndexProvider.

Bug: 112608186
Test: robotests
Change-Id: I0ff16d44bb7b6ad148d3d35f09ca0da0163f73f4

src/com/android/settings/applications/DefaultAppSettings.java

@@ -101,16 +101,6 @@ public class DefaultAppSettings extends DashboardFragment {
                     return Arrays.asList(sir);
                 }
 
-                @Override
-                public List<String> getNonIndexableKeys(Context context) {
-                    List<String> keys = super.getNonIndexableKeys(context);
-                    keys.add(KEY_ASSIST_VOICE_INPUT);
-                    // TODO (b/38230148) Remove these keys when we can differentiate work results
-                    keys.add(DefaultWorkPhonePreferenceController.KEY);
-                    keys.add(DefaultWorkBrowserPreferenceController.KEY);
-                    return keys;
-                }
-
                 @Override
                 public List<AbstractPreferenceController> createPreferenceControllers(
                         Context context) {