Actually use the cache for names and icons.

Fixes the flashes in name and icon in Battery usage screen when refreshing.
Bug: 8219466

Some earlier refactoring must have messed up the cache's scope. It will now
avoid reloading name and icon if already present in the cache.

Change-Id: I99c1f14dd53828dcb74cf12c02c47628e2e64d30

src/com/android/settings/fuelgauge/PowerUsageSummary.java

@@ -178,6 +178,8 @@ public class PowerUsageSummary extends PreferenceFragment implements Runnable {
         super.onDestroy();
         if (getActivity().isChangingConfigurations()) {
             sStatsXfer = mStats;
+        } else {
+            BatterySipper.sUidCache.clear();
         }
     }