[Settings] Code refactor

1. Fix comments
2. Split test case

Bug: 147338143
Test: make RunSettingsRoboTests ROBOTEST_FILTER=DataUsageListTest
Change-Id: I017a3ac8a716e69eb4d9c3e30e20363a215563a2

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

@@ -96,7 +96,7 @@ public class BillingCyclePreference extends Preference
     }
 
     /**
-     * Implementation of MobileDataEnabledListener.Client
+     * Implementation of {@code MobileDataEnabledListener.Client}
      */
     public void onMobileDataEnabledChange() {
         updateEnabled();

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

@@ -240,7 +240,7 @@ public class CellDataPreference extends CustomDialogPreferenceCompat
             };
 
     /**
-     * Implementation of MobileDataEnabledListener.Client
+     * Implementation of {@code MobileDataEnabledListener.Client}
     */
     @VisibleForTesting
     public void onMobileDataEnabledChange() {

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

@@ -201,7 +201,6 @@ public class DataUsageList extends DataUsageBaseFragment
     public void onDestroy() {
         mUidDetailProvider.clearCache();
         mUidDetailProvider = null;
-        mDataStateListener.stop();
 
         super.onDestroy();
     }
@@ -232,7 +231,7 @@ public class DataUsageList extends DataUsageBaseFragment
     }
 
     /**
-     * Implementation of MobileDataEnabledListener.Client
+     * Implementation of {@code MobileDataEnabledListener.Client}
      */
     public void onMobileDataEnabledChange() {
         updatePolicy();

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

@@ -78,7 +78,7 @@ public class DataUsageSummary extends DataUsageBaseFragment implements DataUsage
         super.onCreate(icicle);
         Context context = getContext();
 
-        // enable ProxySubscriptionMgr with Lifecycle support for all controllers
+        // Enable ProxySubscriptionMgr with Lifecycle support for all controllers
         // live within this fragment
         mProxySubscriptionMgr = ProxySubscriptionManager.getInstance(context);
         mProxySubscriptionMgr.setLifecycle(getLifecycle());