Make notifier settings combobox a real combobox.

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 361810989f8b096bce3ee7ebda8b9f1c00c50b86..2fcd7b69029beb56a6c1040ecbc5272c6562189a 100644
--- a/ui/base/models/combobox_model.h
+++ b/ui/base/models/combobox_model.h
@@ -15,6 +15,8 @@ class ComboboxModelObserver;
 // A data model for a combo box.
 class UI_BASE_EXPORT ComboboxModel {
  public:
+  virtual ~ComboboxModel() {}
+
   // Returns the number of items in the combo box.
   virtual int GetItemCount() const = 0;
 
@@ -35,9 +37,6 @@ class UI_BASE_EXPORT ComboboxModel {
   // Adds/removes an observer. Override if model supports mutation.
   virtual void AddObserver(ComboboxModelObserver* observer) {}
   virtual void RemoveObserver(ComboboxModelObserver* observer) {}
-
- protected:
-  virtual ~ComboboxModel() {}
 };
 
 }  // namespace ui