ash: Add GetItemIndexForType() function to ShelfModel.

ash/shelf/shelf_model.h

Index: ash/shelf/shelf_model.h
diff --git a/ash/shelf/shelf_model.h b/ash/shelf/shelf_model.h
index 58e931ab9cf3f10206d57863c642b88b0795e76c..cf51a017da90aee55195ccf3e8b0c84fd2ec0906 100644
--- a/ash/shelf/shelf_model.h
+++ b/ash/shelf/shelf_model.h
@@ -47,6 +47,11 @@ class ASH_EXPORT ShelfModel {
   // Returns the index of the item by id.
   int ItemIndexByID(LauncherID id) const;
 
+  // Returns the |index| of the item matching |type| in |items_|.
+  // Returns -1 if the matching item is not found.
+  // Note: Requires a linear search.
+  int GetItemIndexForType(LauncherItemType type);
+
   // Returns the index of the first panel or the index where the first panel
   // would go if there are no panels.
   int FirstPanelIndex() const;