Fix race condition and optimize categoryUpdater refresh

- In SettingsActivity, do not call updateCategories() if nothing
  changed.
- In SummaryLoader, create a mapping between tile key and summary. This
  is necessary to handle a race condition where category is refreshed
  after summary load.
- In DashboardSummary, refresh Tile's summary to latest cache value
  everytime category is refreshed.

Change-Id: I61389b8ba614ba7e34939325bada6e1bd6fa6709
Fix: 63149109
Test: robotests

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

@@ -294,10 +294,12 @@ public class DashboardSummary extends InstrumentedFragment
 
         final DashboardCategory category = mDashboardFeatureProvider.getTilesForCategory(
                 CategoryKey.CATEGORY_HOMEPAGE);
+        mSummaryLoader.updateSummaryToCache(category);
         if (suggestions != null) {
             mAdapter.setCategoriesAndSuggestions(category, suggestions);
         } else {
             mAdapter.setCategory(category);
         }
     }
+
 }