Add GetDefaultIndex() 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 a746e5311a0c8e75670760da174e5dfe41cff254..022a67c6a7d3613b6971090817fa69dfd0175fb8 100644
--- a/ui/base/models/combobox_model.h
+++ b/ui/base/models/combobox_model.h
@@ -6,11 +6,12 @@
 #define UI_BASE_MODELS_COMBOBOX_MODEL_H_
 
 #include "base/string16.h"
+#include "ui/base/ui_export.h"
 
 namespace ui {
 
 // A data model for a combo box.
-class ComboboxModel {
+class UI_EXPORT ComboboxModel {
  public:
   // Returns the number of items in the combo box.
   virtual int GetItemCount() const = 0;
@@ -18,6 +19,10 @@ class ComboboxModel {
   // Returns the string at the specified index.
   virtual string16 GetItemAt(int index) = 0;
 
+  // The index of the item that is selected by default (before user
+  // interaction).
+  virtual int GetDefaultIndex() const;
+
  protected:
   virtual ~ComboboxModel() {}
 };