Add storage dashborad page.

Refactor shared dashboard page display logic between storage and
system page.

Bug: 31800690
Test: RunSettingsRoboTests

Change-Id: I7eb86f590b79ab871bdb383fb2f5326790beb193

src/com/android/settings/dashboard/DashboardFeatureProvider.java

@@ -35,6 +35,11 @@ public interface DashboardFeatureProvider {
      */
     DashboardCategory getTilesForHomepage();
 
+    /**
+     * Get tiles (wrapped in {@link DashboardCategory}) for storage category.
+     */
+    DashboardCategory getTilesForStorageCategory();
+
     /**
      * Get tiles (wrapped in {@link DashboardCategory}) for system category.
      */