After uninstall, remove last item in Launcher folder

ui/app_list/app_list_model_unittest.cc

Index: ui/app_list/app_list_model_unittest.cc
diff --git a/ui/app_list/app_list_model_unittest.cc b/ui/app_list/app_list_model_unittest.cc
index a81e5043ca0494adcda1323f97a7c8b73411b209..64edc6bcc85ecd999fcda1d8cb1ccb34accaea56 100644
--- a/ui/app_list/app_list_model_unittest.cc
+++ b/ui/app_list/app_list_model_unittest.cc
@@ -438,6 +438,37 @@ TEST_F(AppListModelFolderTest, MoveItemFromFolderToFolder) {
   ASSERT_TRUE(folder2);
 }
 
+TEST_F(AppListModelFolderTest, UninstallFolderItems) {
+  model_.AddItem(new AppListItem("Item 0"));
+  model_.AddItem(new AppListItem("Item 1"));
+  model_.AddItem(new AppListItem("Item 2"));
+  AppListFolderItem* folder1 = static_cast<AppListFolderItem*>(model_.AddItem(
+      new AppListFolderItem("folder1", AppListFolderItem::FOLDER_TYPE_NORMAL)));
+  EXPECT_EQ("Item 0,Item 1,Item 2,folder1", GetModelContents());
+
+  // Move all items to folder1.
+  model_.MoveItemToFolderAt(model_.top_level_item_list()->item_at(0),
+                            folder1->id(), syncer::StringOrdinal());
+  model_.MoveItemToFolderAt(model_.top_level_item_list()->item_at(0),
+                            folder1->id(),
+                            folder1->item_list()->item_at(0)->position());
+  model_.MoveItemToFolderAt(model_.top_level_item_list()->item_at(0),
+                            folder1->id(),
+                            folder1->item_list()->item_at(0)->position());

[stevenjb, 2015/03/25 22:24:01]

This is a little unclear, relying on the fact that moving an item also removes
items from the list making item_at(0) different each time.

None of these operations should delete the items constructed at the beginning of
this test. It might be more clear (and concise) to use CreateAndAddItem:
  AppListItem* item1 = model_.CreateAndAddItem("Item 0");
  ...
  model_.MoveItemToFolderAt(item1, folder_id, item1->position());

[Greg Levin, 2015/03/26 19:45:11]

Done.
(I find the current version more unclear, but only because I don't understand
how "position" encodes information.  My new code wouldn't work if "position"
were "index", but it's clearly something else.)

[stevenjb, 2015/03/30 17:23:59]

'position' is a StringOrdinal, which uses strings like 'a', 'b' to provide
ordering that allows something to be inserted between 'a' and 'b' at 'am'.

[Greg Levin, 2015/03/30 23:08:52]

Ok, thanks.  I'll ask for more detail if I ever need to dig deeper into it.

+  EXPECT_EQ("Item 2,Item 1,Item 0", GetItemListContents(folder1->item_list()));
+  EXPECT_EQ("folder1", GetModelContents());
+
+  // Delete Item 2 from folder.
+  model_.DeleteUninstalledItem("Item 2");
+  EXPECT_EQ("Item 1,Item 0", GetItemListContents(folder1->item_list()));
+  EXPECT_EQ("folder1", GetModelContents());
+
+  // Delete Item 1 from folder, should reparent Item 0 and delete folder1.
+  model_.DeleteUninstalledItem("Item 1");
+  EXPECT_EQ(nullptr, model_.FindItem("folder1"));
+  EXPECT_EQ("Item 0", GetModelContents());
+}

[stevenjb, 2015/03/25 22:24:01]

We should also add a test that creates a single item folder and uninstalls the
item.

[Greg Levin, 2015/03/26 19:45:11]

Done.

+
 TEST_F(AppListModelFolderTest, FindItemInFolder) {
   AppListFolderItem* folder =
       new AppListFolderItem("folder1", AppListFolderItem::FOLDER_TYPE_NORMAL);