Make ComboboxModelObserver a base::CheckedObserver

This allows ObserverList checking for ComboboxModel subclasses, which
have also been updated.

BUG=963982

Change-Id: Idc3b8a853261a1afd8f0c9132d34d1a681b10204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614756Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660616}

chrome/browser/ui/bookmarks/recently_used_folders_combo_model.h

@@ -88,7 +88,7 @@ class RecentlyUsedFoldersComboModel : public ui::ComboboxModel,
   // The index of the original parent folder.
   int node_parent_index_;
 
-  base::ObserverList<ui::ComboboxModelObserver>::Unchecked observers_;
+  base::ObserverList<ui::ComboboxModelObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(RecentlyUsedFoldersComboModel);
 };

components/autofill/core/browser/ui/address_combobox_model.h

@@ -72,7 +72,7 @@ class AddressComboboxModel : public ui::ComboboxModel {
   std::string default_selected_guid_;
 
   // To be called when the data for the given country code was loaded.
-  base::ObserverList<ui::ComboboxModelObserver>::Unchecked observers_;
+  base::ObserverList<ui::ComboboxModelObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AddressComboboxModel);
 };

components/autofill/core/browser/ui/region_combobox_model.h

@@ -70,7 +70,7 @@ class RegionComboboxModel : public ui::ComboboxModel {
   std::vector<std::pair<std::string, std::string>> regions_;
 
   // To be called when the data for the given country code was loaded.
-  base::ObserverList<ui::ComboboxModelObserver>::Unchecked observers_;
+  base::ObserverList<ui::ComboboxModelObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(RegionComboboxModel);
 };

ui/base/models/combobox_model_observer.h

@@ -5,6 +5,7 @@
 #ifndef UI_BASE_MODELS_COMBOBOX_MODEL_OBSERVER_H_
 #define UI_BASE_MODELS_COMBOBOX_MODEL_OBSERVER_H_
 
+#include "base/observer_list_types.h"
 #include "ui/base/ui_base_export.h"
 
 namespace ui {
@@ -12,14 +13,14 @@ namespace ui {
 class ComboboxModel;
 
 // Observer for the ComboboxModel.
-class UI_BASE_EXPORT ComboboxModelObserver {
+class UI_BASE_EXPORT ComboboxModelObserver : public base::CheckedObserver {
  public:
   // Invoked when |model| has changed in some way. The observer should assume
   // everything changed.
   virtual void OnComboboxModelChanged(ComboboxModel* model) = 0;
 
  protected:
-  virtual ~ComboboxModelObserver() {}
+  ~ComboboxModelObserver() override = default;
 };
 
 }  // namespace ui

ui/views/controls/combobox/combobox_unittest.cc

@@ -124,7 +124,7 @@ class TestComboboxModel : public ui::ComboboxModel {
       observer.OnComboboxModelChanged(this);
   }
 
-  base::ObserverList<ui::ComboboxModelObserver>::Unchecked observers_;
+  base::ObserverList<ui::ComboboxModelObserver> observers_;
   std::set<int> separators_;
   int item_count_ = kItemCount;
 
@@ -162,7 +162,7 @@ class VectorComboboxModel : public ui::ComboboxModel {
   }
 
  private:
-  base::ObserverList<ui::ComboboxModelObserver>::Unchecked observers_;
+  base::ObserverList<ui::ComboboxModelObserver> observers_;
   int default_index_ = 0;
   std::vector<std::string>* const values_;