Add |position| to AppListItemModel and add AppListItemList (Take 2)

This adds a |position_| member to AppListItemModel in preparation for
syncing the app list independent of extensions.

It also moves some common code in AppListModel and AppListFolderItem
into AppListItemList, which ensures that |position_| is keept up to date.

This implementation keeps all position maintenance in AppListItemList
and uses AppListItemListObserver to allow ExtensonAppItem to
(temporarily) override the positioning logic.

BUG=305024
For as/shell OWNER:

R=jennyz@chromium.org, xiyuan@chromium.org
TBR=jamescook@chromium.org

Review URL: https://codereview.chromium.org/50003002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231923 0039d316-1c4b-4281-b951-d872f2087c98

33 files changed, 705 insertions, 339 deletions

diff --git a/ash/shell/app_list.cc b/ash/shell/app_list.cc
index 7448de4..fe62d21 100644
--- a/ash/shell/app_list.cc
+++ b/ash/shell/app_list.cc
@@ -16,6 +16,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "ui/app_list/app_list_item_list.h"
 #include "ui/app_list/app_list_item_model.h"
 #include "ui/app_list/app_list_model.h"
 #include "ui/app_list/app_list_view_delegate.h"
@@ -195,14 +196,14 @@ class ExampleAppListViewDelegate : public app_list::AppListViewDelegate {
   ExampleAppListViewDelegate() : model_(NULL) {}
 
  private:
-  void PopulateApps(app_list::AppListModel::Apps* apps) {
+  void PopulateApps(app_list::AppListItemList* item_list) {
     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);
-      apps->Add(new WindowTypeLauncherItem(id, type));
+      item_list->AddItem(new WindowTypeLauncherItem(id, type));
     }
   }
 
@@ -233,7 +234,7 @@ class ExampleAppListViewDelegate : public app_list::AppListViewDelegate {
 
   virtual void InitModel(app_list::AppListModel* model) OVERRIDE {
     model_ = model;
-    PopulateApps(model_->apps());
+    PopulateApps(model_->item_list());
     DecorateSearchBox(model_->search_box());
   }
 
diff --git a/chrome/browser/ui/app_list/extension_app_item.cc b/chrome/browser/ui/app_list/extension_app_item.cc
index 20d3f1c..dbeaa11 100644
--- a/chrome/browser/ui/app_list/extension_app_item.cc
+++ b/chrome/browser/ui/app_list/extension_app_item.cc
@@ -85,13 +85,7 @@ ExtensionAppItem::ExtensionAppItem(Profile* profile,
   Reload();
   GetExtensionSorting(profile_)->EnsureValidOrdinals(extension_id_,
                                                      syncer::StringOrdinal());
-  // Set |sort_order_|. Use '_' as a separator to ensure a_a preceeds aa_a.
-  // (StringOrdinal uses 'a'-'z').
-  const syncer::StringOrdinal& page =
-      GetExtensionSorting(profile_)->GetPageOrdinal(extension_id_);
-  const syncer::StringOrdinal& launch =
-     GetExtensionSorting(profile_)->GetAppLaunchOrdinal(extension_id_);
-  sort_order_ = page.ToInternalValue() + '_' + launch.ToInternalValue();
+  UpdatePositionFromExtensionOrdering();
 }
 
 ExtensionAppItem::~ExtensionAppItem() {
@@ -169,6 +163,7 @@ void ExtensionAppItem::Move(const ExtensionAppItem* prev,
   service->extension_prefs()->SetAppDraggedByUser(extension_id_);
   sorting->SetPageOrdinal(extension_id_, page);
   service->OnExtensionMoved(extension_id_, prev_id, next_id);
+  UpdatePositionFromExtensionOrdering();
 }
 
 const Extension* ExtensionAppItem::GetExtension() const {
@@ -240,10 +235,6 @@ void ExtensionAppItem::ExtensionEnableFlowAborted(bool user_initiated) {
   controller_->OnCloseExtensionPrompt();
 }
 
-std::string ExtensionAppItem::GetSortOrder() const {
-  return sort_order_;
-}
-
 void ExtensionAppItem::Activate(int event_flags) {
   // |extension| could be NULL when it is being unloaded for updating.
   const Extension* extension = GetExtension();
@@ -280,3 +271,12 @@ const char* ExtensionAppItem::GetAppType() const {
 void ExtensionAppItem::ExecuteLaunchCommand(int event_flags) {
   Launch(event_flags);
 }
+
+void ExtensionAppItem::UpdatePositionFromExtensionOrdering() {
+  const syncer::StringOrdinal& page =
+      GetExtensionSorting(profile_)->GetPageOrdinal(extension_id_);
+  const syncer::StringOrdinal& launch =
+     GetExtensionSorting(profile_)->GetAppLaunchOrdinal(extension_id_);
+  set_position(syncer::StringOrdinal(
+      page.ToInternalValue() + launch.ToInternalValue()));
+}
diff --git a/chrome/browser/ui/app_list/extension_app_item.h b/chrome/browser/ui/app_list/extension_app_item.h
index eb56f42..362a016 100644
--- a/chrome/browser/ui/app_list/extension_app_item.h
+++ b/chrome/browser/ui/app_list/extension_app_item.h
@@ -85,7 +85,6 @@ class ExtensionAppItem : public app_list::AppListItemModel,
   virtual void ExtensionEnableFlowAborted(bool user_initiated) OVERRIDE;
 
   // Overridden from AppListItemModel:
-  virtual std::string GetSortOrder() const OVERRIDE;
   virtual void Activate(int event_flags) OVERRIDE;
   virtual ui::MenuModel* GetContextMenuModel() OVERRIDE;
   virtual const char* GetAppType() const OVERRIDE;
@@ -93,6 +92,9 @@ class ExtensionAppItem : public app_list::AppListItemModel,
   // Overridden from app_list::AppContextMenuDelegate:
   virtual void ExecuteLaunchCommand(int event_flags) OVERRIDE;
 
+  // Set the position from the extension ordering.
+  void UpdatePositionFromExtensionOrdering();
+
   Profile* profile_;
   const std::string extension_id_;
   AppListControllerDelegate* controller_;
@@ -110,11 +112,6 @@ class ExtensionAppItem : public app_list::AppListItemModel,
   // Whether or not this app is a platform app.
   bool is_platform_app_;
 
-  // Cache initial sort order. Sort order is not synced with the extensions
-  // app ordering once apps are loaded. This will be ignored (or overridden)
-  // once the app list is synced.
-  std::string sort_order_;
-
   DISALLOW_COPY_AND_ASSIGN(ExtensionAppItem);
 };
 
diff --git a/chrome/browser/ui/app_list/extension_app_model_builder.cc b/chrome/browser/ui/app_list/extension_app_model_builder.cc
index 1f17f6d..63e29a8 100644
--- a/chrome/browser/ui/app_list/extension_app_model_builder.cc
+++ b/chrome/browser/ui/app_list/extension_app_model_builder.cc
@@ -48,13 +48,13 @@ ExtensionAppModelBuilder::ExtensionAppModelBuilder(
       model_(model),
       highlighted_app_pending_(false),
       tracker_(NULL) {
-  model_->apps()->AddObserver(this);
+  model_->item_list()->AddObserver(this);
   SwitchProfile(profile);  // Builds the model.
 }
 
 ExtensionAppModelBuilder::~ExtensionAppModelBuilder() {
   OnShutdown();
-  model_->apps()->RemoveObserver(this);
+  model_->item_list()->RemoveObserver(this);
 }
 
 void ExtensionAppModelBuilder::OnBeginExtensionInstall(
@@ -123,7 +123,7 @@ void ExtensionAppModelBuilder::OnExtensionUnloaded(const Extension* extension) {
 
 void ExtensionAppModelBuilder::OnExtensionUninstalled(
     const Extension* extension) {
-  model_->DeleteItem(extension->id());
+  model_->item_list()->DeleteItem(extension->id());
 }
 
 void ExtensionAppModelBuilder::OnAppsReordered() {
@@ -162,12 +162,7 @@ void ExtensionAppModelBuilder::SwitchProfile(Profile* profile) {
   profile_ = profile;
 
   // Delete any extension apps.
-  app_list::AppListModel::Apps* app_list = model_->apps();
-  for (int i = static_cast<int>(app_list->item_count()) - 1; i >= 0; --i) {
-    app_list::AppListItemModel* item = app_list->GetItemAt(i);
-    if (item->GetAppType() == ExtensionAppItem::kAppType)
-      app_list->DeleteAt(i);
-  }
+  model_->item_list()->DeleteItemsByType(ExtensionAppItem::kAppType);
 
   if (tracker_)
     tracker_->RemoveObserver(this);
@@ -204,7 +199,7 @@ void ExtensionAppModelBuilder::PopulateApps() {
 }
 
 void ExtensionAppModelBuilder::InsertApp(ExtensionAppItem* app) {
-  model_->AddItem(app);
+  model_->item_list()->AddItem(app);
 }
 
 void ExtensionAppModelBuilder::SetHighlightedApp(
@@ -223,7 +218,8 @@ void ExtensionAppModelBuilder::SetHighlightedApp(
 
 ExtensionAppItem* ExtensionAppModelBuilder::GetExtensionAppItem(
     const std::string& extension_id) {
-  app_list::AppListItemModel* item = model_->FindItem(extension_id);
+  app_list::AppListItemModel* item =
+      model_->item_list()->FindItem(extension_id);
   LOG_IF(ERROR, item &&
          item->GetAppType() != ExtensionAppItem::kAppType)
       << "App Item matching id: " << extension_id
@@ -242,39 +238,33 @@ void ExtensionAppModelBuilder::UpdateHighlight() {
   highlighted_app_pending_ = false;
 }
 
-void ExtensionAppModelBuilder::ListItemsAdded(size_t start, size_t count) {
-}
-
-void ExtensionAppModelBuilder::ListItemsRemoved(size_t start, size_t count) {
-}
-
-void ExtensionAppModelBuilder::ListItemMoved(size_t index,
-                                             size_t target_index) {
-  app_list::AppListModel::Apps* app_list = model_->apps();
-  app_list::AppListItemModel* item = app_list->GetItemAt(target_index);
+void ExtensionAppModelBuilder::OnListItemMoved(
+    size_t from_index,
+    size_t to_index,
+    app_list::AppListItemModel* item) {
+  // This will get called from AppListItemList::ListItemMoved after
+  // set_position is called for the item.
+  app_list::AppListItemList* item_list = model_->item_list();
   if (item->GetAppType() != ExtensionAppItem::kAppType)
     return;
 
   ExtensionAppItem* prev = NULL;
-  for (size_t idx = target_index; idx > 1; --idx) {
-    app_list::AppListItemModel* item = app_list->GetItemAt(idx - 1);
+  for (size_t idx = to_index; idx > 0; --idx) {
+    app_list::AppListItemModel* item = item_list->item_at(idx - 1);
     if (item->GetAppType() == ExtensionAppItem::kAppType) {
       prev = static_cast<ExtensionAppItem*>(item);
       break;
     }
   }
   ExtensionAppItem* next = NULL;
-  for (size_t idx = target_index; idx < app_list->item_count() - 1; ++idx) {
-    app_list::AppListItemModel* item = app_list->GetItemAt(idx + 1);
+  for (size_t idx = to_index; idx < item_list->item_count() - 1; ++idx) {
+    app_list::AppListItemModel* item = item_list->item_at(idx + 1);
     if (item->GetAppType() == ExtensionAppItem::kAppType) {
       next = static_cast<ExtensionAppItem*>(item);
       break;
     }
   }
+  // item->Move will call set_position, overriding the item's position.
   if (prev || next)
     static_cast<ExtensionAppItem*>(item)->Move(prev, next);
 }
-
-void ExtensionAppModelBuilder::ListItemsChanged(size_t start, size_t count) {
-  NOTREACHED();
-}
diff --git a/chrome/browser/ui/app_list/extension_app_model_builder.h b/chrome/browser/ui/app_list/extension_app_model_builder.h
index 50cfb9e..48452ee 100644
--- a/chrome/browser/ui/app_list/extension_app_model_builder.h
+++ b/chrome/browser/ui/app_list/extension_app_model_builder.h
@@ -30,7 +30,7 @@ class ImageSkia;
 // This class populates and maintains the given |model| with information from
 // |profile|.
 class ExtensionAppModelBuilder : public extensions::InstallObserver,
-                                 public ui::ListModelObserver {
+                                 public app_list::AppListItemListObserver {
  public:
   ExtensionAppModelBuilder(Profile* profile,
                            app_list::AppListModel* model,
@@ -65,11 +65,10 @@ class ExtensionAppModelBuilder : public extensions::InstallObserver,
       const std::string& extension_id) OVERRIDE;
   virtual void OnShutdown() OVERRIDE;
 
-  // ui::ListModelObserver
-  virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE;
-  virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE;
-  virtual void ListItemMoved(size_t index, size_t target_index) OVERRIDE;
-  virtual void ListItemsChanged(size_t start, size_t count) OVERRIDE;
+  // AppListItemListObserver
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               app_list::AppListItemModel* item) OVERRIDE;
 
   // Adds apps in |extensions| to |apps|.
   void AddApps(const ExtensionSet* extensions, ExtensionAppList* apps);
diff --git a/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc b/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
index bfd3cdd..2354c83 100644
--- a/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
+++ b/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
@@ -32,10 +32,10 @@ const char kPackagedApp2Id[] = "jlklkagmeajbjiobondfhiekepofmljl";
 // Get a string of all apps in |model| joined with ','.
 std::string GetModelContent(app_list::AppListModel* model) {
   std::string content;
-  for (size_t i = 0; i < model->apps()->item_count(); ++i) {
+  for (size_t i = 0; i < model->item_list()->item_count(); ++i) {
     if (i > 0)
       content += ',';
-    content += model->apps()->GetItemAt(i)->title();
+    content += model->item_list()->item_at(i)->title();
   }
   return content;
 }
@@ -285,15 +285,15 @@ TEST_F(ExtensionAppModelBuilderTest, OrdinalConfilicts) {
 
 TEST_F(ExtensionAppModelBuilderTest, SwitchProfile) {
   ExtensionAppModelBuilder builder(profile_.get(), model_.get(), NULL);
-  EXPECT_EQ(kDefaultAppCount, model_->apps()->item_count());
+  EXPECT_EQ(kDefaultAppCount, model_->item_list()->item_count());
 
   // Switch to a profile with no apps, ensure all apps are removed.
   TestingProfile::Builder profile_builder;
   scoped_ptr<TestingProfile> profile2(profile_builder.Build());
   builder.SwitchProfile(profile2.get());
-  EXPECT_EQ(0u, model_->apps()->item_count());
+  EXPECT_EQ(0u, model_->item_list()->item_count());
 
   // Switch back to the main profile, ensure apps are restored.
   builder.SwitchProfile(profile_.get());
-  EXPECT_EQ(kDefaultAppCount, model_->apps()->item_count());
+  EXPECT_EQ(kDefaultAppCount, model_->item_list()->item_count());
 }
diff --git a/chrome/browser/ui/app_list/fast_show_pickler.cc b/chrome/browser/ui/app_list/fast_show_pickler.cc
index 80b2c0f..0119b03 100644
--- a/chrome/browser/ui/app_list/fast_show_pickler.cc
+++ b/chrome/browser/ui/app_list/fast_show_pickler.cc
@@ -207,23 +207,23 @@ scoped_ptr<Pickle> FastShowPickler::PickleAppListModelForFastShow(
     return scoped_ptr<Pickle>();
   if (!result->WriteBool(model->signed_in()))
     return scoped_ptr<Pickle>();
-  if (!result->WriteInt((int) model->apps()->item_count()))
+  if (!result->WriteInt((int) model->item_list()->item_count()))
     return scoped_ptr<Pickle>();
-  for (size_t i = 0; i < model->apps()->item_count(); ++i) {
-    if (!PickleAppListItemModel(result.get(), model->apps()->GetItemAt(i)))
+  for (size_t i = 0; i < model->item_list()->item_count(); ++i) {
+    if (!PickleAppListItemModel(result.get(), model->item_list()->item_at(i)))
       return scoped_ptr<Pickle>();
   }
   return result.Pass();
 }
 
 void FastShowPickler::CopyOver(AppListModel* src, AppListModel* dest) {
-  dest->apps()->DeleteAll();
+  dest->item_list()->DeleteItemsByType(NULL /* all items */);
   dest->SetSignedIn(src->signed_in());
-  for (size_t i = 0; i < src->apps()->item_count(); i++) {
-    AppListItemModel* src_item = src->apps()->GetItemAt(i);
+  for (size_t i = 0; i < src->item_list()->item_count(); i++) {
+    AppListItemModel* src_item = src->item_list()->item_at(i);
     AppListItemModel* dest_item = new AppListItemModel(src_item->id());
     CopyOverItem(src_item, dest_item);
-    dest->apps()->Add(dest_item);
+    dest->item_list()->AddItem(dest_item);
   }
 }
 
@@ -248,7 +248,7 @@ FastShowPickler::UnpickleAppListModelForFastShow(Pickle* pickle) {
     scoped_ptr<AppListItemModel> item(UnpickleAppListItemModel(&it).Pass());
     if (!item)
       return scoped_ptr<AppListModel>();
-    model->apps()->Add(item.release());
+    model->item_list()->AddItem(item.release());
   }
 
   return model.Pass();
diff --git a/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc b/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
index e87fe89..580c3a5 100644
--- a/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
+++ b/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
@@ -17,17 +17,17 @@ using app_list::AppListModel;
 class AppListModelPicklerUnitTest : public testing::Test {
  protected:
   void CheckIsSame(AppListModel* m1, AppListModel* m2) {
-    ASSERT_EQ(m1->apps()->item_count(), m2->apps()->item_count());
+    ASSERT_EQ(m1->item_list()->item_count(), m2->item_list()->item_count());
     ASSERT_EQ(m1->signed_in(), m2->signed_in());
-    for (size_t i = 0; i < m1->apps()->item_count(); i++) {
-      ASSERT_EQ(m1->apps()->GetItemAt(i)->id(),
-                m2->apps()->GetItemAt(i)->id());
-      ASSERT_EQ(m1->apps()->GetItemAt(i)->title(),
-                m2->apps()->GetItemAt(i)->title());
-      ASSERT_EQ(m1->apps()->GetItemAt(i)->full_name(),
-                m2->apps()->GetItemAt(i)->full_name());
-      CompareImages(m1->apps()->GetItemAt(i)->icon(),
-                    m2->apps()->GetItemAt(i)->icon());
+    for (size_t i = 0; i < m1->item_list()->item_count(); i++) {
+      ASSERT_EQ(m1->item_list()->item_at(i)->id(),
+                m2->item_list()->item_at(i)->id());
+      ASSERT_EQ(m1->item_list()->item_at(i)->title(),
+                m2->item_list()->item_at(i)->title());
+      ASSERT_EQ(m1->item_list()->item_at(i)->full_name(),
+                m2->item_list()->item_at(i)->full_name());
+      CompareImages(m1->item_list()->item_at(i)->icon(),
+                    m2->item_list()->item_at(i)->icon());
     }
   }
 
@@ -79,7 +79,7 @@ TEST_F(AppListModelPicklerUnitTest, OneItem) {
   AppListModel model;
   AppListItemModel* app1 = new AppListItemModel("abc");
   app1->SetTitleAndFullName("ht", "hello, there");
-  model.apps()->Add(app1);
+  model.item_list()->AddItem(app1);
 
   DoConsistencyChecks(&model);
 }
@@ -88,11 +88,11 @@ TEST_F(AppListModelPicklerUnitTest, TwoItems) {
   AppListModel model;
   AppListItemModel* app1 = new AppListItemModel("abc");
   app1->SetTitleAndFullName("ht", "hello, there");
-  model.apps()->Add(app1);
+  model.item_list()->AddItem(app1);
 
   AppListItemModel* app2 = new AppListItemModel("abc2");
   app2->SetTitleAndFullName("ht2", "hello, there 2");
-  model.apps()->Add(app2);
+  model.item_list()->AddItem(app2);
 
   DoConsistencyChecks(&model);
 }
@@ -102,11 +102,11 @@ TEST_F(AppListModelPicklerUnitTest, Images) {
   AppListItemModel* app1 = new AppListItemModel("abc");
   app1->SetTitleAndFullName("ht", "hello, there");
   app1->SetIcon(MakeImage(), true);
-  model.apps()->Add(app1);
+  model.item_list()->AddItem(app1);
 
   AppListItemModel* app2 = new AppListItemModel("abc2");
   app2->SetTitleAndFullName("ht2", "hello, there 2");
-  model.apps()->Add(app2);
+  model.item_list()->AddItem(app2);
 
   DoConsistencyChecks(&model);
 }
@@ -116,7 +116,7 @@ TEST_F(AppListModelPicklerUnitTest, EmptyImage) {
   AppListItemModel* app1 = new AppListItemModel("abc");
   app1->SetTitleAndFullName("ht", "hello, there");
   app1->SetIcon(gfx::ImageSkia(), true);
-  model.apps()->Add(app1);
+  model.item_list()->AddItem(app1);
 
   DoConsistencyChecks(&model);
 }
diff --git a/ui/app_list/DEPS b/ui/app_list/DEPS
index bfb1162..bd3bf14 100644
--- a/ui/app_list/DEPS
+++ b/ui/app_list/DEPS
@@ -2,6 +2,7 @@ include_rules = [
   "+grit/ui_resources.h",
   "+grit/ui_strings.h",
   "+skia",
+  "+sync",
   "+third_party/skia",
   # Allow inclusion of third-party code:
   "+third_party/GTM", # Google Toolbox for Mac.
diff --git a/ui/app_list/app_list.gyp b/ui/app_list/app_list.gyp
index 90864a7..15bd6e1 100644
--- a/ui/app_list/app_list.gyp
+++ b/ui/app_list/app_list.gyp
@@ -31,6 +31,9 @@
         'app_list_export.h',
         'app_list_folder_item.cc',
         'app_list_folder_item.h',
+        'app_list_item_list.cc',
+        'app_list_item_list.h',
+        'app_list_item_list_observer.h',
         'app_list_item_model.cc',
         'app_list_item_model.h',
         'app_list_item_model_observer.h',
diff --git a/ui/app_list/app_list_folder_item.cc b/ui/app_list/app_list_folder_item.cc
index 95e5530..e7c505a 100644
--- a/ui/app_list/app_list_folder_item.cc
+++ b/ui/app_list/app_list_folder_item.cc
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 #include "ui/app_list/app_list_folder_item.h"
+
+#include "ui/app_list/app_list_item_list.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/image/canvas_image_source.h"
 #include "ui/gfx/image/image_skia_operations.h"
@@ -91,38 +93,14 @@ class FolderImageSource : public gfx::CanvasImageSource {
 
 AppListFolderItem::AppListFolderItem(const std::string& id)
     : AppListItemModel(id),
-      apps_(new Apps) {
+      item_list_(new AppListItemList) {
+  item_list_->AddObserver(this);
 }
 
 AppListFolderItem::~AppListFolderItem() {
   for (size_t i = 0; i < top_items_.size(); ++i)
     top_items_[i]->RemoveObserver(this);
-}
-
-void AppListFolderItem::AddItem(AppListItemModel* item) {
-  std::string sort_order = item->GetSortOrder();
-  // Note: ui::ListModel is not a sorted list.
-  size_t index = 0;
-  for (; index < apps_->item_count(); ++index) {
-    if (sort_order < apps_->GetItemAt(index)->GetSortOrder())
-      break;
-  }
-  apps_->AddAt(index, item);
-  if (index <= kNumTopApps)
-    UpdateTopItems();
-}
-
-void AppListFolderItem::DeleteItem(const std::string& id) {
-  for (size_t i = 0; i < apps_->item_count(); ++i) {
-    AppListItemModel* item = apps_->GetItemAt(i);
-    if (item->id() == id) {
-      scoped_ptr<AppListItemModel> to_be_deleted(apps_->RemoveAt(i));
-      DCHECK(item == to_be_deleted.get());
-      if (i <= kNumTopApps)
-        UpdateTopItems();
-      return;
-    }
-  }
+  item_list_->RemoveObserver(this);
 }
 
 void AppListFolderItem::UpdateIcon() {
@@ -137,12 +115,6 @@ void AppListFolderItem::UpdateIcon() {
   SetIcon(icon, false);
 }
 
-std::string AppListFolderItem::GetSortOrder() const {
-  // For now, put folders at the end of the list.
-  // TODO(stevenjb): Implement synced app list ordering.
-  return "zzzzzzzz";
-}
-
 void AppListFolderItem::Activate(int event_flags) {
   // Folder handling is implemented by the View, so do nothing.
 }
@@ -175,13 +147,33 @@ void AppListFolderItem::ItemIsInstallingChanged() {
 void AppListFolderItem::ItemPercentDownloadedChanged() {
 }
 
+void AppListFolderItem::OnListItemAdded(size_t index,
+                                        AppListItemModel* item) {
+  if (index <= kNumTopApps)
+    UpdateTopItems();
+}
+
+void AppListFolderItem::OnListItemRemoved(size_t index,
+                                          AppListItemModel* item) {
+  if (index <= kNumTopApps)
+    UpdateTopItems();
+}
+
+void AppListFolderItem::OnListItemMoved(size_t from_index,
+                                        size_t to_index,
+                                        AppListItemModel* item) {
+  if (from_index <= kNumTopApps || to_index <= kNumTopApps)
+    UpdateTopItems();
+}
+
 void AppListFolderItem::UpdateTopItems() {
   for (size_t i = 0; i < top_items_.size(); ++i)
     top_items_[i]->RemoveObserver(this);
   top_items_.clear();
 
-  for (size_t i = 0; i < kNumTopApps && i < apps_->item_count(); ++i) {
-    AppListItemModel* item = apps_->GetItemAt(i);
+  for (size_t i = 0;
+       i < kNumTopApps && i < item_list_->item_count(); ++i) {
+    AppListItemModel* item = item_list_->item_at(i);
     item->AddObserver(this);
     top_items_.push_back(item);
   }
diff --git a/ui/app_list/app_list_folder_item.h b/ui/app_list/app_list_folder_item.h
index db078ea..dd2ce7b 100644
--- a/ui/app_list/app_list_folder_item.h
+++ b/ui/app_list/app_list_folder_item.h
@@ -6,55 +6,56 @@
 #define UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_
 
 #include "ui/app_list/app_list_export.h"
+#include "ui/app_list/app_list_item_list_observer.h"
 #include "ui/app_list/app_list_item_model.h"
 #include "ui/app_list/app_list_item_model_observer.h"
 #include "ui/base/models/list_model.h"
 
 namespace app_list {
 
+class AppListItemList;
+
 // AppListFolderItem implements the model/controller for folders.
 class APP_LIST_EXPORT AppListFolderItem : public AppListItemModel,
+                                          public AppListItemListObserver,
                                           public AppListItemModelObserver {
  public:
-  typedef ui::ListModel<AppListItemModel> Apps;
-
   explicit AppListFolderItem(const std::string& id);
   virtual ~AppListFolderItem();
 
-  // Adds |item| to |apps_|. Takes ownership of |item|.
-  void AddItem(AppListItemModel* item);
-
-  // Finds |item| in |apps_| and deletes it.
-  void DeleteItem(const std::string& id);
-
   // Updates the folder's icon.
   void UpdateIcon();
 
-  Apps* apps() { return apps_.get(); }
+  AppListItemList* item_list() { return item_list_.get(); }
+
+  static const char kAppType[];
 
+ private:
   // AppListItemModel
-  virtual std::string GetSortOrder() const OVERRIDE;
   virtual void Activate(int event_flags) OVERRIDE;
   virtual const char* GetAppType() const OVERRIDE;
   virtual ui::MenuModel* GetContextMenuModel() OVERRIDE;
 
-  // AppListItemModelObserver overrides:
+  // AppListItemModelObserver
   virtual void ItemIconChanged() OVERRIDE;
   virtual void ItemTitleChanged() OVERRIDE;
   virtual void ItemHighlightedChanged() OVERRIDE;
   virtual void ItemIsInstallingChanged() OVERRIDE;
   virtual void ItemPercentDownloadedChanged() OVERRIDE;
 
-  static const char kAppType[];
-
- private:
-  typedef std::vector<AppListItemModel*> AppListItemList;
+  // AppListItemListObserver
+  virtual void OnListItemAdded(size_t index, AppListItemModel* item) OVERRIDE;
+  virtual void OnListItemRemoved(size_t index,
+                                 AppListItemModel* item) OVERRIDE;;
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItemModel* item) OVERRIDE;
 
   void UpdateTopItems();
 
-  scoped_ptr<Apps> apps_;
+  scoped_ptr<AppListItemList> item_list_;
   // Top items for generating folder icon.
-  AppListItemList top_items_;
+  std::vector<AppListItemModel*> top_items_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListFolderItem);
 };
diff --git a/ui/app_list/app_list_item_list.cc b/ui/app_list/app_list_item_list.cc
new file mode 100644
index 0000000..29578f2
--- /dev/null
+++ b/ui/app_list/app_list_item_list.cc
@@ -0,0 +1,132 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/app_list/app_list_item_list.h"
+
+#include "ui/app_list/app_list_item_model.h"
+
+namespace app_list {
+
+AppListItemList::AppListItemList() {
+}
+
+AppListItemList::~AppListItemList() {
+}
+
+void AppListItemList::AddObserver(AppListItemListObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void AppListItemList::RemoveObserver(AppListItemListObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+AppListItemModel* AppListItemList::FindItem(const std::string& id) {
+  for (size_t i = 0; i < app_list_items_.size(); ++i) {
+    AppListItemModel* item = app_list_items_[i];
+    if (item->id() == id)
+      return item;
+  }
+  return NULL;
+}
+
+size_t AppListItemList::AddItem(AppListItemModel* item) {
+  size_t index = GetItemSortOrderIndex(item);
+  app_list_items_.insert(app_list_items_.begin() + index, item);
+  FOR_EACH_OBSERVER(AppListItemListObserver,
+                    observers_,
+                    OnListItemAdded(index, item));
+  return index;
+}
+
+void AppListItemList::DeleteItem(const std::string& id) {
+  for (size_t i = 0; i < app_list_items_.size(); ++i) {
+    AppListItemModel* item = app_list_items_[i];
+    if (item->id() == id) {
+      DeleteItemAt(i);
+      break;
+    }
+  }
+}
+
+void AppListItemList::DeleteItemsByType(const char* type) {
+  for (int i = static_cast<int>(app_list_items_.size()) - 1;
+       i >= 0; --i) {
+    AppListItemModel* item = app_list_items_[i];
+    if (!type || item->GetAppType() == type)
+      DeleteItemAt(i);
+  }
+}
+
+void AppListItemList::MoveItem(size_t from_index, size_t to_index) {
+  DCHECK_LT(from_index, item_count());
+  DCHECK_LT(to_index, item_count());
+  if (from_index == to_index)
+    return;
+
+  AppListItemModel* target_item = app_list_items_[from_index];
+  app_list_items_.weak_erase(app_list_items_.begin() + from_index);
+  app_list_items_.insert(app_list_items_.begin() + to_index, target_item);
+
+  // Update position
+  AppListItemModel* prev = to_index > 0 ? app_list_items_[to_index - 1] : NULL;
+  AppListItemModel* next = to_index < app_list_items_.size() - 1 ?
+      app_list_items_[to_index + 1] : NULL;
+  CHECK_NE(prev, next);
+
+  // It is possible that items were added with the same ordinal. Rather than
+  // resolving a potentially complicated chain of conflicts, just set the
+  // ordinal before |next| (which will place it before both items).
+  if (prev && next && prev->position().Equals(next->position()))
+    prev = NULL;
+
+  VLOG(2) << "Move: " << target_item->position().ToDebugString()
+          << " Prev: " << (prev ? prev->position().ToDebugString() : "(none)")
+          << " Next: " << (next ? next->position().ToDebugString() : "(none)");
+  if (!prev)
+    target_item->set_position(next->position().CreateBefore());
+  else if (!next)
+    target_item->set_position(prev->position().CreateAfter());
+  else
+    target_item->set_position(prev->position().CreateBetween(next->position()));
+  FOR_EACH_OBSERVER(AppListItemListObserver,
+                    observers_,
+                    OnListItemMoved(from_index, to_index, target_item));
+}
+
+// AppListItemList private
+
+void AppListItemList::DeleteItemAt(size_t index) {
+  DCHECK_LT(index, item_count());
+  AppListItemModel* item = app_list_items_[index];
+  app_list_items_.weak_erase(app_list_items_.begin() + index);
+  FOR_EACH_OBSERVER(AppListItemListObserver,
+                    observers_,
+                    OnListItemRemoved(index, item));
+  delete item;
+}
+
+size_t AppListItemList::GetItemSortOrderIndex(AppListItemModel* item) {
+  syncer::StringOrdinal position = item->position();
+  if (!position.IsValid()) {
+    size_t nitems = app_list_items_.size();
+    if (nitems == 0) {
+      position = syncer::StringOrdinal::CreateInitialOrdinal();
+    } else {
+      position = app_list_items_[nitems - 1]->position().CreateAfter();
+    }
+    item->set_position(position);
+    return nitems;
+  }
+  // Note: app_list_items_ is sorted by convention, but sorting is not enforced
+  // (items' positions might be changed outside this class).
+  size_t index = 0;
+  for (; index < app_list_items_.size(); ++index) {
+    if (position.LessThan(app_list_items_[index]->position()))
+      break;
+  }
+  return index;
+}
+
+}  // namespace app_list
diff --git a/ui/app_list/app_list_item_list.h b/ui/app_list/app_list_item_list.h
new file mode 100644
index 0000000..6b033c9
--- /dev/null
+++ b/ui/app_list/app_list_item_list.h
@@ -0,0 +1,72 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_APP_LIST_APP_LIST_ITEM_LIST_H_
+#define UI_APP_LIST_APP_LIST_ITEM_LIST_H_
+
+#include <string>
+
+#include "base/memory/scoped_vector.h"
+#include "base/observer_list.h"
+#include "ui/app_list/app_list_export.h"
+#include "ui/app_list/app_list_item_list_observer.h"
+
+namespace app_list {
+
+class AppListItemModel;
+
+// Class to manage items in the app list. Used both by AppListModel and
+// AppListFolderItem. Manages the position ordinal of items in the list, and
+// notifies observers when items in the list are added / deleted / moved.
+class APP_LIST_EXPORT AppListItemList {
+ public:
+  AppListItemList();
+  virtual ~AppListItemList();
+
+  void AddObserver(AppListItemListObserver* observer);
+  void RemoveObserver(AppListItemListObserver* observer);
+
+  // Find item matching |id|. NOTE: Requires a linear search.
+  AppListItemModel* FindItem(const std::string& id);
+
+  // Adds |item| to the end of |app_list_items_|. Takes ownership of |item|.
+  // Triggers observers_.OnListItemAdded(). Returns the index of the added item.
+  size_t AddItem(AppListItemModel* item);
+
+  // Finds item matching |id| in |app_list_items_| (linear search) and deletes
+  // it. Triggers observers_.OnListItemRemoved() after removing the item from
+  // the list and before deleting it.
+  void DeleteItem(const std::string& id);
+
+  // Deletes all items matching |type| which must be a statically defined
+  // type descriptor, e.g. AppListFolderItem::kAppType. If |type| is NULL,
+  // deletes all items. Triggers observers_.OnListItemRemoved() for each item
+  // as for DeleteItem.
+  void DeleteItemsByType(const char* type);
+
+  // Moves item at |from_index| to |to_index|.
+  // Triggers observers_.OnListItemMoved().
+  void MoveItem(size_t from_index, size_t to_index);
+
+  AppListItemModel* item_at(size_t index) { return app_list_items_[index]; }
+  size_t item_count() const { return app_list_items_.size(); }
+
+ private:
+  // Deletes item at |index| and signals observers.
+  void DeleteItemAt(size_t index);
+
+  // Returns the index at which to insert |item| in |app_list_items_| based on
+  // |item|->position(). If |item|->position() is not valid, returns
+  // |app_list_items_|.item_count() and sets |item|->position() appropriately.
+  size_t GetItemSortOrderIndex(AppListItemModel* item);
+
+  ScopedVector<AppListItemModel> app_list_items_;
+  ObserverList<AppListItemListObserver> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(AppListItemList);
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_APP_LIST_ITEM_LIST_H_
diff --git a/ui/app_list/app_list_item_list_observer.h b/ui/app_list/app_list_item_list_observer.h
new file mode 100644
index 0000000..bca7e90
--- /dev/null
+++ b/ui/app_list/app_list_item_list_observer.h
@@ -0,0 +1,34 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_APP_LIST_APP_LIST_ITEM_LIST_OBSERVER_H_
+#define UI_APP_LIST_APP_LIST_ITEM_LIST_OBSERVER_H_
+
+#include "base/basictypes.h"
+
+namespace app_list {
+
+class AppListItemModel;
+
+class APP_LIST_EXPORT AppListItemListObserver {
+ public:
+  // Triggered after |item| has been added to the list at |index|.
+  virtual void OnListItemAdded(size_t index, AppListItemModel* item) {}
+
+  // Triggered after an item has been removed from the list at |index|, just
+  // before the item is deleted.
+  virtual void OnListItemRemoved(size_t index, AppListItemModel* item) {}
+
+  // Triggered after |item| has been moved from |from_index| to |to_index|.
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItemModel* item) {}
+
+ protected:
+  virtual ~AppListItemListObserver() {}
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_APP_LIST_ITEM_LIST_OBSERVER_H_
diff --git a/ui/app_list/app_list_item_model.cc b/ui/app_list/app_list_item_model.cc
index 87b6969..1846f5e 100644
--- a/ui/app_list/app_list_item_model.cc
+++ b/ui/app_list/app_list_item_model.cc
@@ -73,10 +73,6 @@ void AppListItemModel::RemoveObserver(AppListItemModelObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
-std::string AppListItemModel::GetSortOrder() const {
-  return "";
-}
-
 void AppListItemModel::Activate(int event_flags) {
 }
 
diff --git a/ui/app_list/app_list_item_model.h b/ui/app_list/app_list_item_model.h
index 859b348..505bbb6 100644
--- a/ui/app_list/app_list_item_model.h
+++ b/ui/app_list/app_list_item_model.h
@@ -9,6 +9,7 @@
 
 #include "base/basictypes.h"
 #include "base/observer_list.h"
+#include "sync/api/string_ordinal.h"
 #include "ui/app_list/app_list_export.h"
 #include "ui/gfx/image/image_skia.h"
 
@@ -46,14 +47,15 @@ class APP_LIST_EXPORT AppListItemModel {
   int percent_downloaded() const { return percent_downloaded_; }
 
   const std::string& id() const { return id_; }
+  const syncer::StringOrdinal& position() const { return position_; }
+  void set_position(const syncer::StringOrdinal& new_position) {
+    DCHECK(new_position.IsValid());
+    position_ = new_position;
+  }
 
   void AddObserver(AppListItemModelObserver* observer);
   void RemoveObserver(AppListItemModelObserver* observer);
 
-  // Returns a string used for initially sorting the apps (used by
-  // AppListModel::AddItem). Defaults to an empty string.
-  virtual std::string GetSortOrder() const;
-
   // Activates (opens) the item. Does nothing by default.
   virtual void Activate(int event_flags);
 
@@ -67,7 +69,10 @@ class APP_LIST_EXPORT AppListItemModel {
   virtual ui::MenuModel* GetContextMenuModel();
 
  private:
+  friend class AppListModelTest;
+
   const std::string id_;
+  syncer::StringOrdinal position_;
   gfx::ImageSkia icon_;
   bool has_shadow_;
   std::string title_;
diff --git a/ui/app_list/app_list_model.cc b/ui/app_list/app_list_model.cc
index 2464656..40bb8e9 100644
--- a/ui/app_list/app_list_model.cc
+++ b/ui/app_list/app_list_model.cc
@@ -16,7 +16,7 @@ AppListModel::User::User() : active(false) {}
 AppListModel::User::~User() {}
 
 AppListModel::AppListModel()
-    : apps_(new Apps),
+    : item_list_(new AppListItemList),
       search_box_(new SearchBoxModel),
       results_(new SearchResults),
       signed_in_(false),
@@ -61,34 +61,4 @@ void AppListModel::SetSignedIn(bool signed_in) {
                     OnAppListModelSigninStatusChanged());
 }
 
-AppListItemModel* AppListModel::FindItem(const std::string& id) {
-  for (size_t i = 0; i < apps_->item_count(); ++i) {
-    AppListItemModel* item = apps_->GetItemAt(i);
-    if (item->id() == id)
-      return item;
-  }
-  return NULL;
-}
-
-void AppListModel::AddItem(AppListItemModel* item) {
-  std::string sort_order = item->GetSortOrder();
-  // Note: ui::ListModel is not a sorted list.
-  size_t index = 0;
-  for (; index < apps_->item_count(); ++index) {
-    if (sort_order < apps_->GetItemAt(index)->GetSortOrder())
-      break;
-  }
-  apps_->AddAt(index, item);
-}
-
-void AppListModel::DeleteItem(const std::string& id) {
-  for (size_t i = 0; i < apps_->item_count(); ++i) {
-    AppListItemModel* item = apps_->GetItemAt(i);
-    if (item->id() == id) {
-      apps_->DeleteAt(i);
-      return;
-    }
-  }
-}
-
 }  // namespace app_list
diff --git a/ui/app_list/app_list_model.h b/ui/app_list/app_list_model.h
index 2238941..fbc7970 100644
--- a/ui/app_list/app_list_model.h
+++ b/ui/app_list/app_list_model.h
@@ -13,18 +13,20 @@
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "ui/app_list/app_list_export.h"
+#include "ui/app_list/app_list_item_list.h"
 #include "ui/base/models/list_model.h"
 
 namespace app_list {
 
+class AppListItemList;
 class AppListItemModel;
 class AppListModelObserver;
 class SearchBoxModel;
 class SearchResult;
 
-// Master model of app list that consists of three sub models: Apps,
-// SearchBoxModel and SearchResults. The Apps sub model owns a list of
-// AppListItemModel and is displayed in the grid view. SearchBoxModel is
+// Master model of app list that consists of three sub models: AppListItemList,
+// SearchBoxModel and SearchResults. The AppListItemList sub model owns a list
+// of AppListItemModel and is displayed in the grid view. SearchBoxModel is
 // the model for SearchBoxView. SearchResults owns a list of SearchResult.
 class APP_LIST_EXPORT AppListModel {
  public:
@@ -51,7 +53,6 @@ class APP_LIST_EXPORT AppListModel {
     STATUS_SYNCING,  // Syncing apps or installing synced apps.
   };
 
-  typedef ui::ListModel<AppListItemModel> Apps;
   typedef ui::ListModel<SearchResult> SearchResults;
   typedef std::vector<User> Users;
 
@@ -65,18 +66,7 @@ class APP_LIST_EXPORT AppListModel {
   void SetUsers(const Users& profile_menu_items);
   void SetSignedIn(bool signed_in);
 
-  // Find item matching |id|. NOTE: Requires a linear search.
-  AppListItemModel* FindItem(const std::string& id);
-
-  // Adds |item| to |apps_|. Takes ownership of |item|. Uses item->SortOrder()
-  // to insert in the correct place. TODO(stevenjb): Use synced app list order
-  // instead of SortOrder when available: crbug.com/305024.
-  void AddItem(AppListItemModel* item);
-
-  // Finds |item| in |apps_| and deletes it.
-  void DeleteItem(const std::string& id);
-
-  Apps* apps() { return apps_.get(); }
+  AppListItemList* item_list() { return item_list_.get(); }
   SearchBoxModel* search_box() { return search_box_.get(); }
   SearchResults* results() { return results_.get(); }
   Status status() const { return status_; }
@@ -87,8 +77,7 @@ class APP_LIST_EXPORT AppListModel {
   }
 
  private:
-  scoped_ptr<Apps> apps_;
-
+  scoped_ptr<AppListItemList> item_list_;
   scoped_ptr<SearchBoxModel> search_box_;
   scoped_ptr<SearchResults> results_;
 
diff --git a/ui/app_list/app_list_model_unittest.cc b/ui/app_list/app_list_model_unittest.cc
index 02d77a4..01df3e2 100644
--- a/ui/app_list/app_list_model_unittest.cc
+++ b/ui/app_list/app_list_model_unittest.cc
@@ -8,6 +8,7 @@
 
 #include "base/strings/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "ui/app_list/app_list_folder_item.h"
 #include "ui/app_list/app_list_item_model.h"
 #include "ui/app_list/app_list_model_observer.h"
 #include "ui/app_list/test/app_list_test_model.h"
@@ -18,7 +19,7 @@ namespace app_list {
 namespace {
 
 class TestObserver : public AppListModelObserver,
-                     public ui::ListModelObserver {
+                     public AppListItemListObserver {
  public:
   TestObserver()
       : status_changed_count_(0),
@@ -44,22 +45,22 @@ class TestObserver : public AppListModelObserver,
     ++signin_changed_count_;
   }
 
-  // ui::ListModelObserver
-  virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE {
-    items_added_ += count;
+  // AppListItemListObserver
+  virtual void OnListItemAdded(size_t index, AppListItemModel* item) OVERRIDE {
+    items_added_++;
   }
 
-  virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE {
-    items_removed_ += count;
+  virtual void OnListItemRemoved(size_t index,
+                                 AppListItemModel* item) OVERRIDE {
+    items_removed_++;
   }
 
-  virtual void ListItemMoved(size_t index, size_t target_index) OVERRIDE {
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItemModel* item) OVERRIDE {
     items_moved_++;
   }
 
-  virtual void ListItemsChanged(size_t index, size_t target_index) OVERRIDE {
-  }
-
   int status_changed_count() const { return status_changed_count_; }
   int users_changed_count() const { return users_changed_count_; }
   int signin_changed_count() const { return signin_changed_count_; }
@@ -67,6 +68,15 @@ class TestObserver : public AppListModelObserver,
   size_t items_removed() { return items_removed_; }
   size_t items_moved() { return items_moved_; }
 
+  void ResetCounts() {
+    status_changed_count_ = 0;
+    users_changed_count_ = 0;
+    signin_changed_count_ = 0;
+    items_added_ = 0;
+    items_removed_ = 0;
+    items_moved_ = 0;
+  }
+
  private:
   int status_changed_count_;
   int users_changed_count_;
@@ -88,14 +98,19 @@ class AppListModelTest : public testing::Test {
   // testing::Test overrides:
   virtual void SetUp() OVERRIDE {
     model_.AddObserver(&observer_);
-    model_.apps()->AddObserver(&observer_);
+    model_.item_list()->AddObserver(&observer_);
   }
   virtual void TearDown() OVERRIDE {
     model_.RemoveObserver(&observer_);
-    model_.apps()->RemoveObserver(&observer_);
+    model_.item_list()->RemoveObserver(&observer_);
   }
 
  protected:
+  bool ItemObservedByFolder(AppListFolderItem* folder,
+                            AppListItemModel* item) {
+    return item->observers_.HasObserver(folder);
+  }
+
   test::AppListTestModel model_;
   TestObserver observer_;
 
@@ -148,10 +163,10 @@ TEST_F(AppListModelTest, AppsObserver) {
 TEST_F(AppListModelTest, ModelGetItem) {
   const size_t num_apps = 2;
   model_.PopulateApps(num_apps);
-  AppListItemModel* item0 = model_.apps()->GetItemAt(0);
+  AppListItemModel* item0 = model_.item_list()->item_at(0);
   ASSERT_TRUE(item0);
   EXPECT_EQ(model_.GetItemName(0), item0->id());
-  AppListItemModel* item1 = model_.apps()->GetItemAt(1);
+  AppListItemModel* item1 = model_.item_list()->item_at(1);
   ASSERT_TRUE(item1);
   EXPECT_EQ(model_.GetItemName(1), item1->id());
 }
@@ -160,26 +175,137 @@ TEST_F(AppListModelTest, ModelFindItem) {
   const size_t num_apps = 2;
   model_.PopulateApps(num_apps);
   std::string item_name0 = model_.GetItemName(0);
-  AppListItemModel* item0 = model_.FindItem(item_name0);
+  AppListItemModel* item0 = model_.item_list()->FindItem(item_name0);
   ASSERT_TRUE(item0);
   EXPECT_EQ(item_name0, item0->id());
   std::string item_name1 = model_.GetItemName(1);
-  AppListItemModel* item1 = model_.FindItem(item_name1);
+  AppListItemModel* item1 = model_.item_list()->FindItem(item_name1);
   ASSERT_TRUE(item1);
   EXPECT_EQ(item_name1, item1->id());
 }
 
+TEST_F(AppListModelTest, ModelAddItem) {
+  const size_t num_apps = 2;
+  model_.PopulateApps(num_apps);
+  // Adding another item will add it to the end.
+  model_.CreateAndAddItem("Added Item 1");
+  ASSERT_EQ(num_apps + 1, model_.item_list()->item_count());
+  EXPECT_EQ("Added Item 1", model_.item_list()->item_at(num_apps)->id());
+  // Add an item between items 0 and 1.
+  app_list::AppListItemModel* item0 = model_.item_list()->item_at(0);
+  ASSERT_TRUE(item0);
+  app_list::AppListItemModel* item1 = model_.item_list()->item_at(1);
+  ASSERT_TRUE(item1);
+  app_list::AppListItemModel* item2 =
+      model_.CreateItem("Added Item 2", "Added Item 2");
+  item2->set_position(item0->position().CreateBetween(item1->position()));
+  model_.item_list()->AddItem(item2);
+  EXPECT_EQ(num_apps + 2, model_.item_list()->item_count());
+  EXPECT_EQ("Added Item 2", model_.item_list()->item_at(1)->id());
+}
+
 TEST_F(AppListModelTest, ModelMoveItem) {
   const size_t num_apps = 3;
   model_.PopulateApps(num_apps);
   // Adding another item will add it to the end.
   model_.CreateAndAddItem("Inserted Item");
-  ASSERT_EQ(num_apps + 1, model_.apps()->item_count());
+  ASSERT_EQ(num_apps + 1, model_.item_list()->item_count());
   // Move it to the position 1.
-  model_.apps()->Move(num_apps, 1);
-  AppListItemModel* item = model_.apps()->GetItemAt(1);
+  model_.item_list()->MoveItem(num_apps, 1);
+  AppListItemModel* item = model_.item_list()->item_at(1);
   ASSERT_TRUE(item);
   EXPECT_EQ("Inserted Item", item->id());
 }
 
+TEST_F(AppListModelTest, ModelRemoveItem) {
+  const size_t num_apps = 4;
+  model_.PopulateApps(num_apps);
+  // Remove an item in the middle.
+  model_.item_list()->DeleteItem(model_.GetItemName(1));
+  EXPECT_EQ(num_apps - 1, model_.item_list()->item_count());
+  EXPECT_EQ(1u, observer_.items_removed());
+  // Remove the first item in the list.
+  model_.item_list()->DeleteItem(model_.GetItemName(0));
+  EXPECT_EQ(num_apps - 2, model_.item_list()->item_count());
+  EXPECT_EQ(2u, observer_.items_removed());
+  // Remove the last item in the list.
+  model_.item_list()->DeleteItem(model_.GetItemName(num_apps - 1));
+  EXPECT_EQ(num_apps - 3, model_.item_list()->item_count());
+  EXPECT_EQ(3u, observer_.items_removed());
+  // Ensure that the first item is the expected one
+  AppListItemModel* item0 = model_.item_list()->item_at(0);
+  ASSERT_TRUE(item0);
+  EXPECT_EQ(model_.GetItemName(2), item0->id());
+}
+
+TEST_F(AppListModelTest, ModelRemoveItemByType) {
+  const size_t num_apps = 4;
+  model_.PopulateApps(num_apps);
+  model_.item_list()->AddItem(new AppListFolderItem("folder1"));
+  model_.item_list()->AddItem(new AppListFolderItem("folder2"));
+  model_.item_list()->DeleteItemsByType(test::AppListTestModel::kAppType);
+  EXPECT_EQ(num_apps, observer_.items_removed());
+  EXPECT_EQ(2u, model_.item_list()->item_count());
+  model_.item_list()->DeleteItemsByType(AppListFolderItem::kAppType);
+  EXPECT_EQ(num_apps + 2, observer_.items_removed());
+  EXPECT_EQ(0u, model_.item_list()->item_count());
+  // Delete all items
+  observer_.ResetCounts();
+  model_.PopulateApps(num_apps);
+  model_.item_list()->AddItem(new AppListFolderItem("folder1"));
+  model_.item_list()->AddItem(new AppListFolderItem("folder2"));
+  model_.item_list()->DeleteItemsByType(NULL /* all items */);
+  EXPECT_EQ(num_apps + 2, observer_.items_removed());
+  EXPECT_EQ(0u, model_.item_list()->item_count());
+}
+
+TEST_F(AppListModelTest, AppOrder) {
+  const size_t num_apps = 5;
+  model_.PopulateApps(num_apps);
+  // Ensure order is preserved.
+  for (size_t i = 1; i < num_apps; ++i) {
+    EXPECT_TRUE(model_.item_list()->item_at(i)->position().GreaterThan(
+        model_.item_list()->item_at(i - 1)->position()));
+  }
+  // Move an app
+  model_.item_list()->MoveItem(num_apps - 1, 1);
+  // Ensure order is preserved.
+  for (size_t i = 1; i < num_apps; ++i) {
+    EXPECT_TRUE(model_.item_list()->item_at(i)->position().GreaterThan(
+        model_.item_list()->item_at(i - 1)->position()));
+  }
+}
+
+TEST_F(AppListModelTest, FolderItem) {
+  AppListFolderItem* folder = new AppListFolderItem("folder1");
+  const size_t num_folder_apps = 8;
+  const size_t num_observed_apps = 4;
+  for (int i = 0; static_cast<size_t>(i) < num_folder_apps; ++i) {
+    std::string name = model_.GetItemName(i);
+    folder->item_list()->AddItem(model_.CreateItem(name, name));
+  }
+  // Check that items 0 and 3 are observed.
+  EXPECT_TRUE(ItemObservedByFolder(folder, folder->item_list()->item_at(0)));
+  EXPECT_TRUE(ItemObservedByFolder(
+      folder, folder->item_list()->item_at(num_observed_apps - 1)));
+  // Check that item 4 is not observed.
+  EXPECT_FALSE(ItemObservedByFolder(
+      folder, folder->item_list()->item_at(num_observed_apps)));
+  folder->item_list()->MoveItem(num_observed_apps, 0);
+  // Confirm that everything was moved where expected.
+  EXPECT_EQ(model_.GetItemName(num_observed_apps),
+            folder->item_list()->item_at(0)->id());
+  EXPECT_EQ(model_.GetItemName(0),
+            folder->item_list()->item_at(1)->id());
+  EXPECT_EQ(model_.GetItemName(num_observed_apps - 1),
+            folder->item_list()->item_at(num_observed_apps)->id());
+  // Check that items 0 and 3 are observed.
+  EXPECT_TRUE(ItemObservedByFolder(folder, folder->item_list()->item_at(0)));
+  EXPECT_TRUE(ItemObservedByFolder(
+      folder, folder->item_list()->item_at(num_observed_apps - 1)));
+  // Check that item 4 is not observed.
+  EXPECT_FALSE(ItemObservedByFolder(
+      folder, folder->item_list()->item_at(num_observed_apps)));
+}
+
 }  // namespace app_list
diff --git a/ui/app_list/cocoa/apps_grid_controller.h b/ui/app_list/cocoa/apps_grid_controller.h
index 77ad382..b53c814 100644
--- a/ui/app_list/cocoa/apps_grid_controller.h
+++ b/ui/app_list/cocoa/apps_grid_controller.h
@@ -23,7 +23,7 @@ class AppsGridDelegateBridge;
 @protocol AppsPaginationModelObserver;
 @class AppsCollectionViewDragManager;
 
-// Controls a grid of views, representing AppListModel::Apps sub models.
+// Controls a grid of views, representing AppListItemList sub models.
 APP_LIST_EXPORT
 @interface AppsGridController : NSViewController<GestureScrollDelegate,
                                                  AppListPagerDelegate,
diff --git a/ui/app_list/cocoa/apps_grid_controller.mm b/ui/app_list/cocoa/apps_grid_controller.mm
index 5fad26f..d450ef4 100644
--- a/ui/app_list/cocoa/apps_grid_controller.mm
+++ b/ui/app_list/cocoa/apps_grid_controller.mm
@@ -76,12 +76,11 @@ NSTimeInterval g_scroll_duration = 0.18;
 - (void)updatePageContent:(size_t)pageIndex
                resetModel:(BOOL)resetModel;
 
-// Bridged methods for ui::ListModelObserver.
-- (void)listItemsAdded:(size_t)start
-                 count:(size_t)count;
+// Bridged methods for AppListItemListObserver.
+- (void)listItemAdded:(size_t)index
+                 item:(app_list::AppListItemModel*)item;
 
-- (void)listItemsRemoved:(size_t)start
-                   count:(size_t)count;
+- (void)listItemRemoved:(size_t)index;
 
 - (void)listItemMovedFromIndex:(size_t)fromIndex
                   toModelIndex:(size_t)toIndex;
@@ -93,26 +92,25 @@ NSTimeInterval g_scroll_duration = 0.18;
 
 namespace app_list {
 
-class AppsGridDelegateBridge : public ui::ListModelObserver {
+class AppsGridDelegateBridge : public AppListItemListObserver {
  public:
   AppsGridDelegateBridge(AppsGridController* parent) : parent_(parent) {}
 
  private:
-  // Overridden from ui::ListModelObserver:
-  virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE {
-    [parent_ listItemsAdded:start
-                      count:count];
+  // Overridden from AppListItemListObserver:
+  virtual void OnListItemAdded(size_t index, AppListItemModel* item) OVERRIDE {
+    [parent_ listItemAdded:index
+                      item:item];
   }
-  virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE {
-    [parent_ listItemsRemoved:start
-                        count:count];
+  virtual void OnListItemRemoved(size_t index,
+                                 AppListItemModel* item) OVERRIDE {
+    [parent_ listItemRemoved:index];
   }
-  virtual void ListItemMoved(size_t index, size_t target_index) OVERRIDE {
-    [parent_ listItemMovedFromIndex:index
-                       toModelIndex:target_index];
-  }
-  virtual void ListItemsChanged(size_t start, size_t count) OVERRIDE {
-    NOTREACHED();
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItemModel* item) OVERRIDE {
+    [parent_ listItemMovedFromIndex:from_index
+                       toModelIndex:to_index];
   }
 
   AppsGridController* parent_;  // Weak, owns us.
@@ -188,7 +186,7 @@ class AppsGridDelegateBridge : public ui::ListModelObserver {
 
 - (void)setModel:(scoped_ptr<app_list::AppListModel>)newModel {
   if (model_) {
-    model_->apps()->RemoveObserver(bridge_.get());
+    model_->item_list()->RemoveObserver(bridge_.get());
 
     // Since the model is about to be deleted, and the AppKit objects might be
     // sitting in an NSAutoreleasePool, ensure there are no references to the
@@ -205,9 +203,13 @@ class AppsGridDelegateBridge : public ui::ListModelObserver {
   if (!model_)
     return;
 
-  model_->apps()->AddObserver(bridge_.get());
-  [self listItemsAdded:0
-                 count:model_->apps()->item_count()];
+  model_->item_list()->AddObserver(bridge_.get());
+  for (size_t i = 0; i < model_->item_list()->item_count(); ++i) {
+    app_list::AppListItemModel* itemModel = model_->item_list()->item_at(i);
+    [items_ insertObject:[NSValue valueWithPointer:itemModel]
+                 atIndex:i];
+  }
+  [self updatePages:0];
 }
 
 - (void)setDelegate:(app_list::AppListViewDelegate*)newDelegate {
@@ -522,9 +524,9 @@ class AppsGridDelegateBridge : public ui::ListModelObserver {
   if (itemIndex == modelIndex)
     return;
 
-  model_->apps()->RemoveObserver(bridge_.get());
-  model_->apps()->Move(itemIndex, modelIndex);
-  model_->apps()->AddObserver(bridge_.get());
+  model_->item_list()->RemoveObserver(bridge_.get());
+  model_->item_list()->MoveItem(itemIndex, modelIndex);
+  model_->item_list()->AddObserver(bridge_.get());
 }
 
 - (AppsCollectionViewDragManager*)dragManager {
@@ -535,30 +537,25 @@ class AppsGridDelegateBridge : public ui::ListModelObserver {
   return scheduledScrollPage_;
 }
 
-- (void)listItemsAdded:(size_t)start
-                 count:(size_t)count {
+- (void)listItemAdded:(size_t)index
+                 item:(app_list::AppListItemModel*)itemModel {
   // Cancel any drag, to ensure the model stays consistent.
   [dragManager_ cancelDrag];
 
-  for (size_t i = start; i < start + count; ++i) {
-    app_list::AppListItemModel* itemModel = model_->apps()->GetItemAt(i);
-    [items_ insertObject:[NSValue valueWithPointer:itemModel]
-                 atIndex:i];
-  }
+  [items_ insertObject:[NSValue valueWithPointer:itemModel]
+              atIndex:index];
 
-  [self updatePages:start];
+  [self updatePages:index];
 }
 
-- (void)listItemsRemoved:(size_t)start
-                   count:(size_t)count {
+- (void)listItemRemoved:(size_t)index {
   [dragManager_ cancelDrag];
 
   // Clear the models explicitly to avoid surprises from autorelease.
-  for (size_t i = start; i < start + count; ++i)
-    [[self itemAtIndex:i] setModel:NULL];
+  [[self itemAtIndex:index] setModel:NULL];
 
-  [items_ removeObjectsInRange:NSMakeRange(start, count)];
-  [self updatePages:start];
+  [items_ removeObjectsInRange:NSMakeRange(index, 1)];
+  [self updatePages:index];
 }
 
 - (void)listItemMovedFromIndex:(size_t)fromIndex
diff --git a/ui/app_list/cocoa/apps_grid_controller_unittest.mm b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
index df4e142..5692574 100644
--- a/ui/app_list/cocoa/apps_grid_controller_unittest.mm
+++ b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
@@ -424,7 +424,7 @@ TEST_F(AppsGridControllerTest, EnsureHighlightedVisible) {
 // Test runtime updates: adding items, removing items, and moving items (e.g. in
 // response to app install, uninstall, and chrome sync changes. Also test
 // changing titles and icons.
-TEST_F(AppsGridControllerTest, ModelUpdates) {
+TEST_F(AppsGridControllerTest, ModelUpdate) {
   model()->PopulateApps(2);
   EXPECT_EQ(2u, [[GetPageAt(0) content] count]);
   EXPECT_EQ(std::string("|Item 0,Item 1|"), GetViewContent());
@@ -437,7 +437,7 @@ TEST_F(AppsGridControllerTest, ModelUpdates) {
   EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
 
   // Update the title via the ItemModelObserver.
-  app_list::AppListItemModel* item_model = model()->apps()->GetItemAt(2);
+  app_list::AppListItemModel* item_model = model()->item_list()->item_at(2);
   item_model->SetTitleAndFullName("UpdatedItem", "UpdatedItem");
   EXPECT_NSEQ(@"UpdatedItem", [button title]);
   EXPECT_EQ(std::string("|Item 0,Item 1,UpdatedItem|"), GetViewContent());
@@ -456,9 +456,48 @@ TEST_F(AppsGridControllerTest, ModelUpdates) {
   // Icon should always be resized to 48x48.
   EXPECT_EQ(kTargetImageSize, icon_size.width);
   EXPECT_EQ(kTargetImageSize, icon_size.height);
+}
+
+TEST_F(AppsGridControllerTest, ModelAdd) {
+  model()->PopulateApps(2);
+  EXPECT_EQ(2u, [[GetPageAt(0) content] count]);
+  EXPECT_EQ(std::string("|Item 0,Item 1|"), GetViewContent());
+
+  app_list::AppListItemList* item_list = model()->item_list();
+
+  model()->CreateAndAddItem("Item 2");
+  ASSERT_EQ(3u, item_list->item_count());
+  EXPECT_EQ(3u, [apps_grid_controller_ itemCount]);
+  EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
+
+  // Test adding an item whose position is in the middle.
+  app_list::AppListItemModel* item0 = item_list->item_at(0);
+  app_list::AppListItemModel* item1 = item_list->item_at(1);
+  app_list::AppListItemModel* item3 =
+      model()->CreateItem("Item Three", "Item Three");
+  item3->set_position(item0->position().CreateBetween(item1->position()));
+  item_list->AddItem(item3);
+  EXPECT_EQ(4u, [apps_grid_controller_ itemCount]);
+  EXPECT_EQ(std::string("|Item 0,Item Three,Item 1,Item 2|"), GetViewContent());
+}
+
+TEST_F(AppsGridControllerTest, ModelMove) {
+  model()->PopulateApps(3);
+  EXPECT_EQ(3u, [[GetPageAt(0) content] count]);
+  EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
+
+  // Test swapping items (e.g. rearranging via sync).
+  model()->item_list()->MoveItem(1, 2);
+  EXPECT_EQ(std::string("|Item 0,Item 2,Item 1|"), GetViewContent());
+}
+
+TEST_F(AppsGridControllerTest, ModelRemove) {
+  model()->PopulateApps(3);
+  EXPECT_EQ(3u, [[GetPageAt(0) content] count]);
+  EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
 
   // Test removing an item at the end.
-  model()->apps()->DeleteAt(2);
+  model()->item_list()->DeleteItem("Item 2");
   EXPECT_EQ(2u, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(std::string("|Item 0,Item 1|"), GetViewContent());
 
@@ -466,29 +505,34 @@ TEST_F(AppsGridControllerTest, ModelUpdates) {
   model()->CreateAndAddItem("Item 2");
   EXPECT_EQ(3u, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
-  model()->apps()->DeleteAt(1);
+  model()->item_list()->DeleteItem("Item 1");
   EXPECT_EQ(2u, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(std::string("|Item 0,Item 2|"), GetViewContent());
+}
 
-  // Test inserting in the middle.
-  model()->apps()->AddAt(1, model()->CreateItem("Item One", "Item One"));
-  EXPECT_EQ(3u, [apps_grid_controller_ itemCount]);
-  EXPECT_EQ(std::string("|Item 0,Item One,Item 2|"), GetViewContent());
-
-  // Test swapping items (e.g. rearranging via sync).
-  model()->apps()->Move(1, 2);
-  EXPECT_EQ(std::string("|Item 0,Item 2,Item One|"), GetViewContent());
+TEST_F(AppsGridControllerTest, ModelRemoveAlll) {
+  model()->PopulateApps(3);
+  EXPECT_EQ(3u, [[GetPageAt(0) content] count]);
+  EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
 
   // Test removing multiple items via the model.
-  model()->apps()->DeleteAll();
+  model()->item_list()->DeleteItemsByType(NULL /* all items */);
   EXPECT_EQ(0u, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(std::string("||"), GetViewContent());
+}
 
-  // Test removing the last item when there is one item on the second page.
-  ReplaceTestModel(kItemsPerPage + 1);
+TEST_F(AppsGridControllerTest, ModelRemovePage) {
+  app_list::AppListItemList* item_list = model()->item_list();
+
+  model()->PopulateApps(kItemsPerPage + 1);
+  ASSERT_EQ(kItemsPerPage + 1, item_list->item_count());
   EXPECT_EQ(kItemsPerPage + 1, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(2u, [apps_grid_controller_ pageCount]);
-  model()->apps()->DeleteAt(kItemsPerPage);
+
+  // Test removing the last item when there is one item on the second page.
+  app_list::AppListItemModel* last_item = item_list->item_at(kItemsPerPage);
+  item_list->DeleteItem(last_item->id());
+  EXPECT_EQ(kItemsPerPage, item_list->item_count());
   EXPECT_EQ(kItemsPerPage, [apps_grid_controller_ itemCount]);
   EXPECT_EQ(1u, [apps_grid_controller_ pageCount]);
 }
@@ -499,7 +543,7 @@ TEST_F(AppsGridControllerTest, ItemInstallProgress) {
   EXPECT_EQ(2u, [apps_grid_controller_ pageCount]);
   EXPECT_EQ(0u, [apps_grid_controller_ visiblePage]);
   app_list::AppListItemModel* item_model =
-      model()->apps()->GetItemAt(kItemsPerPage);
+      model()->item_list()->item_at(kItemsPerPage);
 
   // Highlighting an item should activate the page it is on.
   item_model->SetHighlighted(true);
@@ -535,7 +579,7 @@ TEST_F(AppsGridControllerTest, ItemInstallProgress) {
   // Two things can be installing simultaneously. When one starts or completes
   // the model builder will ask for the item to be highlighted.
   app_list::AppListItemModel* alternate_item_model =
-      model()->apps()->GetItemAt(0);
+      model()->item_list()->item_at(0);
   item_model->SetHighlighted(false);
   alternate_item_model->SetHighlighted(true);
   EXPECT_EQ(0u, [apps_grid_controller_ visiblePage]);
@@ -906,8 +950,8 @@ TEST_F(AppsGridControllerTest, ScrollingWhileDragging) {
 
 TEST_F(AppsGridControllerTest, ContextMenus) {
   AppListItemWithMenu* item_two_model = new AppListItemWithMenu("Item Two");
-  model()->apps()->AddAt(0, new AppListItemWithMenu("Item One"));
-  model()->apps()->AddAt(1, item_two_model);
+  model()->item_list()->AddItem(new AppListItemWithMenu("Item One"));
+  model()->item_list()->AddItem(item_two_model);
   EXPECT_EQ(2u, [apps_grid_controller_ itemCount]);
 
   NSCollectionView* page = [apps_grid_controller_ collectionViewAtPageIndex:0];
diff --git a/ui/app_list/cocoa/apps_grid_view_item.mm b/ui/app_list/cocoa/apps_grid_view_item.mm
index b6e4fb5..ccd6b80 100644
--- a/ui/app_list/cocoa/apps_grid_view_item.mm
+++ b/ui/app_list/cocoa/apps_grid_view_item.mm
@@ -80,7 +80,7 @@ class ItemModelObserverBridge : public app_list::AppListItemModelObserver {
 
  private:
   AppsGridViewItem* parent_;  // Weak. Owns us.
-  AppListItemModel* model_;  // Weak. Owned by AppListModel::Apps.
+  AppListItemModel* model_;  // Weak. Owned by AppListModel.
   base::scoped_nsobject<MenuController> context_menu_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(ItemModelObserverBridge);
diff --git a/ui/app_list/test/app_list_test_model.cc b/ui/app_list/test/app_list_test_model.cc
index 6f6bf10..4fd1acc 100644
--- a/ui/app_list/test/app_list_test_model.cc
+++ b/ui/app_list/test/app_list_test_model.cc
@@ -10,6 +10,9 @@
 namespace app_list {
 namespace test {
 
+// static
+const char AppListTestModel::kAppType[] = "FolderItem";
+
 class AppListTestModel::AppListTestItemModel : public AppListItemModel {
  public:
   AppListTestItemModel(const std::string& id, AppListTestModel* model)
@@ -22,6 +25,10 @@ class AppListTestModel::AppListTestItemModel : public AppListItemModel {
     model_->ItemActivated(this);
   }
 
+  virtual const char* GetAppType() const OVERRIDE {
+    return AppListTestModel::kAppType;
+  }
+
  private:
   AppListTestModel* model_;
   DISALLOW_COPY_AND_ASSIGN(AppListTestItemModel);
@@ -38,7 +45,7 @@ std::string AppListTestModel::GetItemName(int id) {
 }
 
 void AppListTestModel::PopulateApps(int n) {
-  int start_index = apps()->item_count();
+  int start_index = item_list()->item_count();
   for (int i = 0; i < n; ++i)
     CreateAndAddItem(GetItemName(start_index + i));
 }
@@ -49,10 +56,10 @@ void AppListTestModel::PopulateAppWithId(int id) {
 
 std::string AppListTestModel::GetModelContent() {
   std::string content;
-  for (size_t i = 0; i < apps()->item_count(); ++i) {
+  for (size_t i = 0; i < item_list()->item_count(); ++i) {
     if (i > 0)
       content += ',';
-    content += apps()->GetItemAt(i)->title();
+    content += item_list()->item_at(i)->title();
   }
   return content;
 }
@@ -60,13 +67,20 @@ std::string AppListTestModel::GetModelContent() {
 AppListItemModel* AppListTestModel::CreateItem(const std::string& title,
                                                const std::string& full_name) {
   AppListItemModel* item = new AppListTestItemModel(title, this);
+  size_t nitems = item_list()->item_count();
+  syncer::StringOrdinal position;
+  if (nitems == 0)
+    position = syncer::StringOrdinal::CreateInitialOrdinal();
+  else
+    position = item_list()->item_at(nitems - 1)->position().CreateAfter();
+  item->set_position(position);
   item->SetTitleAndFullName(title, full_name);
   return item;
 }
 
 void AppListTestModel::CreateAndAddItem(const std::string& title,
                                         const std::string& full_name) {
-  AddItem(CreateItem(title, full_name));
+  item_list()->AddItem(CreateItem(title, full_name));
 }
 
 void AppListTestModel::CreateAndAddItem(const std::string& title) {
@@ -74,7 +88,7 @@ void AppListTestModel::CreateAndAddItem(const std::string& title) {
 }
 
 void AppListTestModel::HighlightItemAt(int index) {
-  AppListItemModel* item = apps()->GetItemAt(index);
+  AppListItemModel* item = item_list()->item_at(index);
   item->SetHighlighted(true);
 }
 
diff --git a/ui/app_list/test/app_list_test_model.h b/ui/app_list/test/app_list_test_model.h
index 548072e..473152e 100644
--- a/ui/app_list/test/app_list_test_model.h
+++ b/ui/app_list/test/app_list_test_model.h
@@ -48,6 +48,8 @@ class AppListTestModel : public AppListModel {
   int activate_count() { return activate_count_; }
   AppListItemModel* last_activated() { return last_activated_; }
 
+  static const char kAppType[];
+
  private:
   class AppListTestItemModel;
 
diff --git a/ui/app_list/views/app_list_folder_view.cc b/ui/app_list/views/app_list_folder_view.cc
index ec6e24f..44d31b8 100644
--- a/ui/app_list/views/app_list_folder_view.cc
+++ b/ui/app_list/views/app_list_folder_view.cc
@@ -55,7 +55,7 @@ AppListFolderView::~AppListFolderView() {
 
 void AppListFolderView::SetAppListFolderItem(AppListFolderItem* folder) {
   folder_item_ = folder;
-  items_grid_view_->SetApps(folder_item_->apps());
+  items_grid_view_->SetItemList(folder_item_->item_list());
   folder_header_view_->SetFolderItem(folder_item_);
 }
 
@@ -93,4 +93,3 @@ void AppListFolderView::NavigateBack(AppListFolderItem* item,
 }
 
 }  // namespace app_list
-
diff --git a/ui/app_list/views/app_list_item_view.h b/ui/app_list/views/app_list_item_view.h
index 311d721..08fe244 100644
--- a/ui/app_list/views/app_list_item_view.h
+++ b/ui/app_list/views/app_list_item_view.h
@@ -105,7 +105,7 @@ class APP_LIST_EXPORT AppListItemView : public views::CustomButton,
   // ui::EventHandler overrides:
   virtual void OnGestureEvent(ui::GestureEvent* event) OVERRIDE;
 
-  AppListItemModel* model_;  // Owned by AppListModel::Apps.
+  AppListItemModel* model_;  // Owned by AppListModel.
 
   AppsGridView* apps_grid_view_;  // Owned by views hierarchy.
   views::ImageView* icon_;  // Owned by views hierarchy.
diff --git a/ui/app_list/views/app_list_main_view.cc b/ui/app_list/views/app_list_main_view.cc
index 0a83325..dd1a30c 100644
--- a/ui/app_list/views/app_list_main_view.cc
+++ b/ui/app_list/views/app_list_main_view.cc
@@ -161,12 +161,12 @@ void AppListMainView::PreloadIcons(PaginationModel* pagination_model,
   const int tiles_per_page = kPreferredCols * kPreferredRows;
   const int start_model_index = selected_page * tiles_per_page;
   const int end_model_index = std::min(
-      static_cast<int>(model_->apps()->item_count()),
+      static_cast<int>(model_->item_list()->item_count()),
       start_model_index + tiles_per_page);
 
   pending_icon_loaders_.clear();
   for (int i = start_model_index; i < end_model_index; ++i) {
-    AppListItemModel* item = model_->apps()->GetItemAt(i);
+    AppListItemModel* item = model_->item_list()->item_at(i);
     if (item->icon().HasRepresentation(scale))
       continue;
 
diff --git a/ui/app_list/views/apps_container_view.cc b/ui/app_list/views/apps_container_view.cc
index ea520b6..6becc49 100644
--- a/ui/app_list/views/apps_container_view.cc
+++ b/ui/app_list/views/apps_container_view.cc
@@ -34,7 +34,7 @@ AppsContainerView::AppsContainerView(AppListMainView* app_list_main_view,
   AddChildView(app_list_folder_view_);
 
   apps_grid_view_->SetModel(model_);
-  apps_grid_view_->SetApps(model_->apps());
+  apps_grid_view_->SetItemList(model_->item_list());
 }
 
 AppsContainerView::~AppsContainerView() {
@@ -88,6 +88,3 @@ void AppsContainerView::SetShowState(ShowState show_state) {
 }
 
 }  // namespace app_list
-
-
-
diff --git a/ui/app_list/views/apps_grid_view.cc b/ui/app_list/views/apps_grid_view.cc
index 09d056f..d8f92c3 100644
--- a/ui/app_list/views/apps_grid_view.cc
+++ b/ui/app_list/views/apps_grid_view.cc
@@ -234,7 +234,7 @@ AppsGridView::AppsGridView(AppsGridViewDelegate* delegate,
                            PaginationModel* pagination_model,
                            content::WebContents* start_page_contents)
     : model_(NULL),
-      apps_(NULL),
+      item_list_(NULL),
       delegate_(delegate),
       pagination_model_(pagination_model),
       page_switcher_view_(new PageSwitcher(pagination_model)),
@@ -273,8 +273,8 @@ AppsGridView::~AppsGridView() {
     model_->RemoveObserver(this);
   pagination_model_->RemoveObserver(this);
 
-  if (apps_)
-    apps_->RemoveObserver(this);
+  if (item_list_)
+    item_list_->RemoveObserver(this);
 }
 
 void AppsGridView::SetLayout(int icon_size, int cols, int rows_per_page) {
@@ -299,12 +299,12 @@ void AppsGridView::SetModel(AppListModel* model) {
   Update();
 }
 
-void AppsGridView::SetApps(AppListModel::Apps* apps) {
-  if (apps_)
-    apps_->RemoveObserver(this);
+void AppsGridView::SetItemList(AppListItemList* item_list) {
+  if (item_list_)
+    item_list_->RemoveObserver(this);
 
-  apps_ = apps;
-  apps_->AddObserver(this);
+  item_list_ = item_list;
+  item_list_->AddObserver(this);
   Update();
 }
 
@@ -631,12 +631,21 @@ void AppsGridView::ViewHierarchyChanged(
 
 void AppsGridView::Update() {
   DCHECK(!selected_view_ && !drag_view_);
-  if (!apps_)
+  if (!item_list_)
     return;
 
   view_model_.Clear();
-  if (apps_ && apps_->item_count())
-    ListItemsAdded(0, apps_->item_count());
+  if (!item_list_->item_count())
+    return;
+  for (size_t i = 0; i < item_list_->item_count(); ++i) {
+    views::View* view = CreateViewForItemAtIndex(i);
+    view_model_.Add(view, i);
+    AddChildView(view);
+  }
+  UpdatePaging();
+  UpdatePulsingBlockViews();
+  Layout();
+  SchedulePaint();
 }
 
 void AppsGridView::UpdatePaging() {
@@ -649,7 +658,7 @@ void AppsGridView::UpdatePaging() {
 
 void AppsGridView::UpdatePulsingBlockViews() {
   const int available_slots =
-      tiles_per_page() - apps_->item_count() % tiles_per_page();
+      tiles_per_page() - item_list_->item_count() % tiles_per_page();
   const int desired = model_->status() == AppListModel::STATUS_SYNCING ?
       available_slots : 0;
 
@@ -671,9 +680,9 @@ void AppsGridView::UpdatePulsingBlockViews() {
 }
 
 views::View* AppsGridView::CreateViewForItemAtIndex(size_t index) {
-  DCHECK_LT(index, apps_->item_count());
+  DCHECK_LT(index, item_list_->item_count());
   AppListItemView* view = new AppListItemView(this,
-                                              apps_->GetItemAt(index));
+                                              item_list_->item_at(index));
   view->SetIconSize(icon_size_);
 #if defined(USE_AURA)
   view->SetPaintToLayer(true);
@@ -1108,10 +1117,10 @@ void AppsGridView::MoveItemInModel(views::View* item_view,
   if (target_model_index == current_model_index)
     return;
 
-  apps_->RemoveObserver(this);
-  apps_->Move(current_model_index, target_model_index);
+  item_list_->RemoveObserver(this);
+  item_list_->MoveItem(current_model_index, target_model_index);
   view_model_.Move(current_model_index, target_model_index);
-  apps_->AddObserver(this);
+  item_list_->AddObserver(this);
 
   if (pagination_model_->selected_page() != target.page)
     pagination_model_->SelectPage(target.page, false);
@@ -1170,14 +1179,12 @@ void AppsGridView::LayoutStartPage() {
   start_page_view_->SetBoundsRect(start_page_bounds);
 }
 
-void AppsGridView::ListItemsAdded(size_t start, size_t count) {
+void AppsGridView::OnListItemAdded(size_t index, AppListItemModel* item) {
   EndDrag(true);
 
-  for (size_t i = start; i < start + count; ++i) {
-    views::View* view = CreateViewForItemAtIndex(i);
-    view_model_.Add(view, i);
-    AddChildView(view);
-  }
+  views::View* view = CreateViewForItemAtIndex(index);
+  view_model_.Add(view, index);
+  AddChildView(view);
 
   UpdatePaging();
   UpdatePulsingBlockViews();
@@ -1185,14 +1192,12 @@ void AppsGridView::ListItemsAdded(size_t start, size_t count) {
   SchedulePaint();
 }
 
-void AppsGridView::ListItemsRemoved(size_t start, size_t count) {
+void AppsGridView::OnListItemRemoved(size_t index, AppListItemModel* item) {
   EndDrag(true);
 
-  for (size_t i = 0; i < count; ++i) {
-    views::View* view = view_model_.view_at(start);
-    view_model_.Remove(start);
-    delete view;
-  }
+  views::View* view = view_model_.view_at(index);
+  view_model_.Remove(index);
+  delete view;
 
   UpdatePaging();
   UpdatePulsingBlockViews();
@@ -1200,18 +1205,16 @@ void AppsGridView::ListItemsRemoved(size_t start, size_t count) {
   SchedulePaint();
 }
 
-void AppsGridView::ListItemMoved(size_t index, size_t target_index) {
+void AppsGridView::OnListItemMoved(size_t from_index,
+                                   size_t to_index,
+                                   AppListItemModel* item) {
   EndDrag(true);
-  view_model_.Move(index, target_index);
+  view_model_.Move(from_index, to_index);
 
   UpdatePaging();
   AnimateToIdealBounds();
 }
 
-void AppsGridView::ListItemsChanged(size_t start, size_t count) {
-  NOTREACHED();
-}
-
 void AppsGridView::TotalPagesChanged() {
 }
 
diff --git a/ui/app_list/views/apps_grid_view.h b/ui/app_list/views/apps_grid_view.h
index 31f2fed..ec66746 100644
--- a/ui/app_list/views/apps_grid_view.h
+++ b/ui/app_list/views/apps_grid_view.h
@@ -48,10 +48,10 @@ class AppsGridViewDelegate;
 class PageSwitcher;
 class PaginationModel;
 
-// AppsGridView displays a grid for AppListModel::Apps sub model.
+// AppsGridView displays a grid for AppListItemList sub model.
 class APP_LIST_EXPORT AppsGridView : public views::View,
                                      public views::ButtonListener,
-                                     public ui::ListModelObserver,
+                                     public AppListItemListObserver,
                                      public PaginationModelObserver,
                                      public AppListModelObserver {
  public:
@@ -78,8 +78,9 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
   // Sets |model| to use. Note this does not take ownership of |model|.
   void SetModel(AppListModel* model);
 
-  // Set |apps| to renders. Note this does not take ownership of |apps|.
-  void SetApps(AppListModel::Apps* apps);
+  // Sets the |item_list| to render. Note this does not take ownership of
+  // |item_list|.
+  void SetItemList(AppListItemList* item_list);
 
   void SetSelectedView(views::View* view);
   void ClearSelectedView(views::View* view);
@@ -250,11 +251,12 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
   virtual void ButtonPressed(views::Button* sender,
                              const ui::Event& event) OVERRIDE;
 
-  // Overridden from ListModelObserver:
-  virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE;
-  virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE;
-  virtual void ListItemMoved(size_t index, size_t target_index) OVERRIDE;
-  virtual void ListItemsChanged(size_t start, size_t count) OVERRIDE;
+  // Overridden from AppListItemListObserver:
+  virtual void OnListItemAdded(size_t index, AppListItemModel* item) OVERRIDE;
+  virtual void OnListItemRemoved(size_t index, AppListItemModel* item) OVERRIDE;
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItemModel* item) OVERRIDE;
 
   // Overridden from PaginationModelObserver:
   virtual void TotalPagesChanged() OVERRIDE;
@@ -272,7 +274,7 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
   void SetViewHidden(views::View* view, bool hide, bool immediate);
 
   AppListModel* model_;  // Owned by AppListView.
-  AppListModel::Apps* apps_;  // Not owned.
+  AppListItemList* item_list_;  // Not owned.
   AppsGridViewDelegate* delegate_;
   PaginationModel* pagination_model_;  // Owned by AppListController.
   PageSwitcher* page_switcher_view_;  // Owned by views hierarchy.
diff --git a/ui/app_list/views/apps_grid_view_unittest.cc b/ui/app_list/views/apps_grid_view_unittest.cc
index 896f076..34c0c77 100644
--- a/ui/app_list/views/apps_grid_view_unittest.cc
+++ b/ui/app_list/views/apps_grid_view_unittest.cc
@@ -108,7 +108,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
     apps_grid_view_->SetLayout(kIconDimension, kCols, kRows);
     apps_grid_view_->SetBoundsRect(gfx::Rect(gfx::Size(kWidth, kHeight)));
     apps_grid_view_->SetModel(model_.get());
-    apps_grid_view_->SetApps(model_->apps());
+    apps_grid_view_->SetItemList(model_->item_list());
 
     test_api_.reset(new AppsGridViewTestApi(apps_grid_view_.get()));
   }
@@ -124,7 +124,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
   }
 
   AppListItemView* GetItemViewForPoint(const gfx::Point& point) {
-    for (size_t i = 0; i < model_->apps()->item_count(); ++i) {
+    for (size_t i = 0; i < model_->item_list()->item_count(); ++i) {
       AppListItemView* view = GetItemViewAt(i);
       if (view->bounds().Contains(point))
         return view;
@@ -133,7 +133,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
   }
 
   gfx::Rect GetItemTileRectAt(int row, int col) {
-    DCHECK_GT(model_->apps()->item_count(), 0u);
+    DCHECK_GT(model_->item_list()->item_count(), 0u);
 
     gfx::Insets insets(apps_grid_view_->GetInsets());
     gfx::Rect rect(gfx::Point(insets.left(), insets.top()),
@@ -206,7 +206,7 @@ TEST_F(AppsGridViewTest, EnsureHighlightedVisible) {
   EXPECT_EQ(1, pagination_model_->selected_page());
 
   // Highlight last one in the model and last page should be selected.
-  model_->HighlightItemAt(model_->apps()->item_count() - 1);
+  model_->HighlightItemAt(model_->item_list()->item_count() - 1);
   EXPECT_EQ(kPages - 1, pagination_model_->selected_page());
 }
 
@@ -218,7 +218,7 @@ TEST_F(AppsGridViewTest, RemoveSelectedLastApp) {
 
   AppListItemView* last_view = GetItemViewAt(kLastItemIndex);
   apps_grid_view_->SetSelectedView(last_view);
-  model_->apps()->DeleteAt(kLastItemIndex);
+  model_->item_list()->DeleteItem(model_->GetItemName(kLastItemIndex));
 
   EXPECT_FALSE(apps_grid_view_->IsSelectedView(last_view));
 
@@ -253,7 +253,7 @@ TEST_F(AppsGridViewTest, MouseDrag) {
 
   // Deleting an item keeps remaining intact.
   SimulateDrag(AppsGridView::MOUSE, from, to);
-  model_->apps()->DeleteAt(1);
+  model_->item_list()->DeleteItem(model_->GetItemName(0));
   apps_grid_view_->EndDrag(false);
   EXPECT_EQ(std::string("Item 1,Item 2,Item 3"),
             model_->GetModelContent());