ui/base/models: Add protected virtual destructor to ComboboxModel.

ui/base/models/combobox_model.h

Index: ui/base/models/combobox_model.h
diff --git a/ui/base/models/combobox_model.h b/ui/base/models/combobox_model.h
index 57dd3c325c97d7896f0e0bf9692cb9b79389cece..4f3f781992e6a8067a9fb0d0343dfd324cd68848 100644
--- a/ui/base/models/combobox_model.h
+++ b/ui/base/models/combobox_model.h
@@ -10,16 +10,17 @@
 
 namespace ui {
 
-// The interface for models backing a combobox.
+// A data model for a combo box.
 class ComboboxModel {
  public:
-  virtual ~ComboboxModel() {}
-
-  // Return the number of items in the combo box.
+  // Returns the number of items in the combo box.
   virtual int GetItemCount() = 0;
 
-  // Return the string that should be used to represent a given item.
+  // Returns the string at the specified index.
   virtual string16 GetItemAt(int index) = 0;
+
+ protected:
+  virtual ~ComboboxModel() {}
 };
 
 }  // namespace ui