Refactor SummaryLoader to set summary on subsetting pages.

- Make a SummaryConsumer interface. Things that needs latest summary
  should implement this interface (DashboardAdapter for homepage,
  DashboardFragment for subsettings). This also decouples SummaryLoader
  from relying on SettingsDrawerActivity.
- Make DashboardFeatureProvider more generic to load DashboardCategory
  by key.

Bug: 31781480
Test: RunSettingsRoboTests
Change-Id: I9c65456fb433a74c352498251e0ccf65da0be1f0

src/com/android/settings/system/SystemDashboardFragment.java

@@ -25,7 +25,7 @@ import com.android.settings.deviceinfo.SystemUpdatePreferenceController;
 import com.android.settings.overlay.FeatureFactory;
 import com.android.settings.search.BaseSearchIndexProvider;
 import com.android.settings.search.Indexable;
-import com.android.settingslib.drawer.DashboardCategory;
+import com.android.settingslib.drawer.CategoryKey;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -62,8 +62,8 @@ public class SystemDashboardFragment extends DashboardFragment {
     }
 
     @Override
-    protected DashboardCategory getDashboardTiles() {
-        return mDashboardFeatureProvider.getTilesForSystemCategory();
+    protected String getCategoryKey() {
+        return CategoryKey.CATEGORY_SYSTEM;
     }
 
     /**