Add remote volume slider conditionally.

Issue before this CL:
RemoteVolumePreferenceController only return available when
it is casting, otherwise return CONDITIONALLY_UNAVAILABLE.
However slice database only index available controllers and keep
this cache. So remote slider won't be indexed if it is not casting
at that time.

As a tmp fix, this CL make controller always return available
unsearchable to make it indexed by database. However only add
that slice if it is casting.

Bug: 130124950
Test: RunSettingsRoboTests
Change-Id: I191144844d6ba7ccbe3dc1c9d19801adb978abc6

src/com/android/settings/panel/VolumePanel.java

@@ -30,6 +30,7 @@ import android.net.Uri;
 import android.provider.Settings;
 
 import com.android.settings.R;
+import com.android.settings.notification.RemoteVolumePreferenceController;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -54,7 +55,9 @@ public class VolumePanel implements PanelContent {
     @Override
     public List<Uri> getSlices() {
         final List<Uri> uris = new ArrayList<>();
-        uris.add(VOLUME_REMOTE_MEDIA_URI);
+        if (RemoteVolumePreferenceController.getActiveRemoteToken(mContext) != null) {
+            uris.add(VOLUME_REMOTE_MEDIA_URI);
+        }
         uris.add(VOLUME_MEDIA_URI);
         uris.add(MEDIA_OUTPUT_INDICATOR_SLICE_URI);
         uris.add(VOLUME_CALL_URI);