Fix flicker for Data Usage page

Both "Mobile data usage" & "Non-carrier data usage".

By,
1. Use summary placeholder for usage amount to avoid shift
2. Before fix CycleListener's onItemSelected() is called multiple times,
   cause the app list to flash, let DataUsageList to handle the dedup
   logic to better handling.
3. Before fix if return from App Usage page, no loading view is
   displayed (only first enter has it), move this to onResume() to fix.
4. Before fix the cycles passed to App Usage page is cached (even when
   the cycles are changed), clear the cache when onResume() to fix.
5. Listener in SpinnerPreference could be null, add safety guard to it.

Cherry-pick from Change-Id: I95e544c46333496f4f30ed77dafa4779b4d66019

Fix: 277162513
Test: manual visual test
Test: Unit test
Change-Id: I50fb79aa3c888651a79fd1d030da554bebb6a660

src/com/android/settings/datausage/CycleAdapter.java

@@ -21,7 +21,6 @@ import com.android.settingslib.net.NetworkCycleData;
 import com.android.settingslib.widget.SettingsSpinnerAdapter;
 
 import java.util.List;
-import java.util.Objects;
 
 public class CycleAdapter extends SettingsSpinnerAdapter<CycleAdapter.CycleItem> {
 
@@ -67,7 +66,7 @@ public class CycleAdapter extends SettingsSpinnerAdapter<CycleAdapter.CycleItem>
      * Rebuild list based on network data. Always selects the newest item,
      * updating the inspection range on chartData.
      */
-    public boolean updateCycleList(List<? extends NetworkCycleData> cycleData) {
+    public void updateCycleList(List<? extends NetworkCycleData> cycleData) {
         mSpinner.setOnItemSelectedListener(mListener);
         // stash away currently selected cycle to try restoring below
         final CycleAdapter.CycleItem previousItem = (CycleAdapter.CycleItem)
@@ -83,16 +82,7 @@ public class CycleAdapter extends SettingsSpinnerAdapter<CycleAdapter.CycleItem>
         if (getCount() > 0) {
             final int position = findNearestPosition(previousItem);
             mSpinner.setSelection(position);
-
-            // only force-update cycle when changed; skipping preserves any
-            // user-defined inspection region.
-            final CycleAdapter.CycleItem selectedItem = getItem(position);
-            if (!Objects.equals(selectedItem, previousItem)) {
-                mListener.onItemSelected(null, null, position, 0);
-                return false;
-            }
         }
-        return true;
     }
 
     /**