Protect AppListItemList Add/Remove and fix sync bugs

ash/shell/app_list.cc

Index: ash/shell/app_list.cc
diff --git a/ash/shell/app_list.cc b/ash/shell/app_list.cc
index 72a0777e6cc6428447cb884cf362ff7fce0ebadb..10e1a6146e1f50fa82ef8639422a6bce3ad8e2f7 100644
--- a/ash/shell/app_list.cc
+++ b/ash/shell/app_list.cc
@@ -198,19 +198,19 @@ class ExampleAppListViewDelegate : public app_list::AppListViewDelegate {
  public:
   ExampleAppListViewDelegate()
       : model_(new app_list::AppListModel) {
-    PopulateApps(model_->item_list());

[tapted, 2014/01/28 11:56:53]

Maybe something to consider, but I guess it's not feasible for
AppListModel::item_list() to return a `const AppListItemList*` (e.g. I think
we'd still want AppListItemList::item_at(..) to return a non-const
`AppListItem*` [e.g. to add/remove obsververs], so it might look weird).

[stevenjb, 2014/01/28 18:28:08]

We specifically don't allow const methods to return non-const pointers. We could
make add/remove observer mutable, but I would just as soon avoid that.

Also, as we add complexity to the model (e.g. pages) we should be moving away
from manipulating the item lists directly and interact only with the model.

+    PopulateApps();
     DecorateSearchBox(model_->search_box());
   }
 
  private:
-  void PopulateApps(app_list::AppListItemList* item_list) {
+  void PopulateApps() {
     for (int i = 0;
          i < static_cast<int>(WindowTypeLauncherItem::LAST_TYPE);
          ++i) {
       WindowTypeLauncherItem::Type type =
           static_cast<WindowTypeLauncherItem::Type>(i);
       std::string id = base::StringPrintf("%d", i);
-      item_list->AddItem(new WindowTypeLauncherItem(id, type));
+      model_->AddItem(new WindowTypeLauncherItem(id, type));
     }
   }