GuidedStepFragment Subclass need explcitly specify a container id for background

After fixed Bug 24570987

Change-Id: I1ec51f8ea39b21e4d547e923386dd357a538ff4a

samples/SupportLeanbackDemos/src/com/example/android/leanback/GuidedStepActivity.java

@@ -106,9 +106,6 @@ public class GuidedStepActivity extends Activity {
                 .build());
     }
 
-    /**
-     * The first fragment is instantiated via XML, so it must be public.
-     */
     public static class FirstStepFragment extends GuidedStepFragment {
         @Override
         public int onProvideTheme() {
@@ -139,6 +136,11 @@ public class GuidedStepActivity extends Activity {
                 getActivity().finish();
             }
         }
+
+        @Override
+        protected int getContainerIdForBackground() {
+            return R.id.lb_guidedstep_background;
+        }
     }
 
     public static class SecondStepFragment extends GuidedStepFragment {

samples/SupportLeanbackDemos/src/com/example/android/leanback/GuidedStepSupportActivity.java

@@ -108,9 +108,6 @@ public class GuidedStepSupportActivity extends FragmentActivity {
                 .build());
     }
 
-    /**
-     * The first fragment is instantiated via XML, so it must be public.
-     */
     public static class FirstStepFragment extends GuidedStepSupportFragment {
         @Override
         public int onProvideTheme() {
@@ -141,6 +138,11 @@ public class GuidedStepSupportActivity extends FragmentActivity {
                 getActivity().finish();
             }
         }
+
+        @Override
+        protected int getContainerIdForBackground() {
+            return R.id.lb_guidedstep_background;
+        }
     }
 
     public static class SecondStepFragment extends GuidedStepSupportFragment {