Register rule for wallpaper entry

We should keep consistent split rule for wallpaper and other home menu
item. So, we create this cl to register the split rule for wallpaper.

Also, I do some minor refactoring in this cl for reusing existing
method and better code quality.

Test: Go to wallpaper, and click back key. App can close.
Fix: 204406425
Fix: 204364572

Change-Id: Ia7de9483b351d1121cc26c4af1cb8a89ad0a16bc

src/com/android/settings/search/SearchResultTrampoline.java

@@ -97,7 +97,7 @@ public class SearchResultTrampoline extends Activity {
         } else if (isFromSettingsIntelligence(callingActivity)) {
             // Register SplitPairRule for SubSettings, set clearTop false to prevent unexpected back
             // navigation behavior.
-            ActivityEmbeddingRulesController.registerSubSettingsPairRuleIfNeeded(this,
+            ActivityEmbeddingRulesController.registerSubSettingsPairRule(this,
                     false /* clearTop */);
             // TODO: pass menu key to homepage
             intent.setFlags(intent.getFlags() & ~Intent.FLAG_ACTIVITY_NEW_TASK);