Remove jank on DND schedule page

Only add/or remove preferences when absolutely needed.
Also fix a 'load data from backend' method that wasn't.

Fixes: 216747934
Test: ZenModeAutomaticRulesPreferenceControllerTest
Test: view schedules page
Test: add schedule
Test: remove schedule
Test: view schedule child page and return to schedules page
Change-Id: I237c2ca7ea89ee6e42354470a76712068a7f4dd7

src/com/android/settings/notification/zen/ZenRulePreference.java

@@ -60,13 +60,15 @@ public class ZenRulePreference extends PrimarySwitchPreference {
 
     public ZenRulePreference(Context context,
             final Map.Entry<String, AutomaticZenRule> ruleEntry,
-            Fragment parent, MetricsFeatureProvider metricsProvider) {
+            Fragment parent, MetricsFeatureProvider metricsProvider,
+            ZenModeBackend backend) {
         super(context);
-        mBackend = ZenModeBackend.getInstance(context);
+        mBackend = backend;
         mContext = context;
         mRule = ruleEntry.getValue();
         mName = mRule.getName();
         mId = ruleEntry.getKey();
+        setKey(mId);
         mParent = parent;
         mPm = mContext.getPackageManager();
         mServiceListing = new ZenServiceListing(mContext, CONFIG);