AcceleratorProvider: Make GetAcceleratorForCommandId const.

ui/base/models/simple_menu_model.h

Index: ui/base/models/simple_menu_model.h
diff --git a/ui/base/models/simple_menu_model.h b/ui/base/models/simple_menu_model.h
index 639830d10717c9a291b91ccd900974b47bc85b76..c86f958bf3175352429e2e0609d4c316e5e3cc93 100644
--- a/ui/base/models/simple_menu_model.h
+++ b/ui/base/models/simple_menu_model.h
@@ -39,7 +39,7 @@ class UI_BASE_EXPORT SimpleMenuModel : public MenuModel {
     // command id has a valid accelerator, false otherwise.
     virtual bool GetAcceleratorForCommandId(
         int command_id,
-        ui::Accelerator* accelerator) = 0;
+        ui::Accelerator* accelerator) const = 0;
 
     // Some command ids have labels, sublabels, minor text and icons that change
     // over time.
@@ -134,7 +134,7 @@ class UI_BASE_EXPORT SimpleMenuModel : public MenuModel {
 
   // Returns the index of the item that has the given |command_id|. Returns
   // -1 if not found.
-  int GetIndexOfCommandId(int command_id);
+  int GetIndexOfCommandId(int command_id) const;
 
   // Overridden from MenuModel:
   bool HasIcons() const override;