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/deviceinfo/StorageDashboardFragment.java

@@ -24,7 +24,7 @@ import com.android.settings.dashboard.DashboardFragment;
 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;
@@ -51,8 +51,8 @@ public class StorageDashboardFragment extends DashboardFragment {
     }
 
     @Override
-    protected DashboardCategory getDashboardTiles() {
-        return mDashboardFeatureProvider.getTilesForStorageCategory();
+    protected String getCategoryKey() {
+        return CategoryKey.CATEGORY_STORAGE;
     }
 
     @Override