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/dashboard/DashboardFeatureProvider.java

@@ -31,19 +31,9 @@ public interface DashboardFeatureProvider {
     boolean isEnabled();
 
     /**
-     * Get tiles (wrapped in {@link DashboardCategory}) for homepage.
+     * Get tiles (wrapped in {@link DashboardCategory}) for key defined in CategoryKey.
      */
-    DashboardCategory getTilesForHomepage();
-
-    /**
-     * Get tiles (wrapped in {@link DashboardCategory}) for storage category.
-     */
-    DashboardCategory getTilesForStorageCategory();
-
-    /**
-     * Get tiles (wrapped in {@link DashboardCategory}) for system category.
-     */
-    DashboardCategory getTilesForSystemCategory();
+    DashboardCategory getTilesForCategory(String key);
 
     /**
      * Get all tiles, grouped by category.