Define ICON_UNAVAILABLE for no icon status

Bug: 147776885
Test: make -j42 RunSettingsRoboTests
Change-Id: I0fd0e203bb7590955d0caf2679ebc78be68b4e50

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

@@ -28,11 +28,13 @@ import java.util.List;
  */
 public interface PanelContent extends Instrumentable {
 
+    int ICON_UNAVAILABLE = -1;
+
     /**
      * @return a icon resource for the title of the Panel.
      */
     default int getIcon() {
-        return -1;
+        return ICON_UNAVAILABLE;
     }
 
     /**

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

@@ -193,7 +193,7 @@ public class PanelFragment extends Fragment {
         loadAllSlices();
 
         final int iconRes = mPanel.getIcon();
-        if (iconRes == -1) {
+        if (iconRes == PanelContent.ICON_UNAVAILABLE) {
             mTitleView.setText(mPanel.getTitle());
         } else {
             mTitleView.setVisibility(View.GONE);