Request SupportFeatureProvider to provide a support tab.

Bug: 28139604

In dashboard container, if supportFeatureProvider is able to provide a
tab, we display it in tabbed layout. Otherwise, display just
DashboardSummary without changing UI.

Change-Id: Ib7601ac925e1315e6b0928d020fe2d09bd389cd7

src/com/android/settings/InstrumentedFragment.java

@@ -32,6 +32,8 @@ public abstract class InstrumentedFragment extends PreferenceFragment {
     // Used by PreferenceActivity for the dummy fragment it adds, no useful data here.
     public static final int PREFERENCE_ACTIVITY_FRAGMENT = UNDECLARED + 2;
 
+    public static final int SUPPORT_FRAGMENT = UNDECLARED + 3;
+
     /**
      * Declare the view of this category.
      *