Added default implementations of GetAcceleratorForCommandId.

ui/base/models/button_menu_item_model.h

Index: ui/base/models/button_menu_item_model.h
diff --git a/ui/base/models/button_menu_item_model.h b/ui/base/models/button_menu_item_model.h
index efe3f8f02de8649394790ce335898e3316576a3d..98a72344d7eb9081283ea709e863e2a49d67e071 100644
--- a/ui/base/models/button_menu_item_model.h
+++ b/ui/base/models/button_menu_item_model.h
@@ -38,10 +38,10 @@ class UI_BASE_EXPORT ButtonMenuItemModel {
     virtual bool DoesCommandIdDismissMenu(int command_id) const;
 
     // Gets the accelerator for the specified command id. Returns true if the
-    // command id has a valid accelerator, false otherwise.
-    virtual bool GetAcceleratorForCommandId(
-        int command_id,
-        ui::Accelerator* accelerator) const = 0;
+    // command id has a valid accelerator, false otherwise. By default, returns
+    // false for all commands.
+    virtual bool GetAcceleratorForCommandId(int command_id,
+                                            ui::Accelerator* accelerator) const;
 
    protected:
     virtual ~Delegate() {}