ash: Add GetItemIndexForType() function to ShelfModel.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 8a2f524bc7b8c4d54012fc2a9ce39ade41e784b2..67340198fe8d62ee785108eb5da56999d832902a 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -43,7 +43,6 @@
 #include "ash/shelf/app_list_shelf_item_delegate.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shelf/shelf_model.h"
-#include "ash/shelf/shelf_model_util.h"
 #include "ash/shelf/shelf_widget.h"
 #include "ash/shell_delegate.h"
 #include "ash/shell_factory.h"
@@ -511,7 +510,7 @@ LauncherDelegate* Shell::GetLauncherDelegate() {
 
     // Finding the shelf model's location of the app list and setting its
     // LauncherItemDelegate.
-    int app_list_index = GetShelfItemIndexForType(TYPE_APP_LIST, *shelf_model_);
+    int app_list_index = shelf_model_->GetItemIndexForType(TYPE_APP_LIST);
     DCHECK_GE(app_list_index, 0);
     LauncherID app_list_id = shelf_model_->items()[app_list_index].id;
     DCHECK(app_list_id);