chore: make BrowserObserver a CheckedObserver

refs: 1053338

atom/browser/ui/atom_menu_model.h

@@ -8,6 +8,7 @@
 #include <map>
 
 #include "base/observer_list.h"
+#include "base/observer_list_types.h"
 #include "ui/base/models/simple_menu_model.h"
 
 namespace atom {
@@ -33,9 +34,9 @@ class AtomMenuModel : public ui::SimpleMenuModel {
         ui::Accelerator* accelerator) const override;
   };
 
-  class Observer {
+  class Observer : public base::CheckedObserver {
    public:
-    virtual ~Observer() {}
+    ~Observer() override {}
 
     // Notifies the menu will open.
     virtual void OnMenuWillShow() {}

atom/browser/ui/tray_icon_observer.h

@@ -8,6 +8,8 @@
 #include <string>
 #include <vector>
 
+#include "base/observer_list_types.h"
+
 namespace gfx {
 class Rect;
 class Point;
@@ -15,7 +17,7 @@ class Point;
 
 namespace atom {
 
-class TrayIconObserver {
+class TrayIconObserver : public base::CheckedObserver {
  public:
   virtual void OnClicked(const gfx::Rect& bounds,
                          const gfx::Point& location,
@@ -36,7 +38,7 @@ class TrayIconObserver {
   virtual void OnMouseMoved(const gfx::Point& location, int modifiers) {}
 
  protected:
-  virtual ~TrayIconObserver() {}
+  ~TrayIconObserver() override {}
 };
 
 }  // namespace atom

atom/browser/ui/views/menu_delegate.h

@@ -70,7 +70,7 @@ class MenuDelegate : public views::MenuDelegate {
   views::MenuButton* button_to_open_ = nullptr;
   bool hold_first_switch_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(MenuDelegate);
 };