Moving install queue updates to worker thread.

This avoids acquiring a lock for upating the sharedPrefs during onResume
as all the logic runs on a single thread.

Bug: 67305604
Change-Id: I1bbea382da9fafb403b4e9508f393f78db28478d

tests/src/com/android/launcher3/model/AddWorkspaceItemsTaskTest.java

@@ -55,7 +55,7 @@ public class AddWorkspaceItemsTaskTest extends BaseModelUpdateTaskTestCase {
         for (ItemInfo item : items) {
             list.add(Pair.create(item, null));
         }
-        return new AddWorkspaceItemsTask(Provider.of(list)) {
+        return new AddWorkspaceItemsTask(list) {
 
             @Override
             protected void updateScreens(Context context, ArrayList<Long> workspaceScreens) { }