Convert DisplayManager to use CheckedObserver

Display observers have historically caused problems on Chrome OS.
They are not performance critical, so converted from UncheckedObserver
to checked observer.

Bug: 842987
Change-Id: I803afb4c6b5a2ef8e2bf1652183a8835243d07ec
Reviewed-on: https://chromium-review.googlesource.com/c/1263338Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597374}

ui/display/display_change_notifier.h

@@ -32,7 +32,7 @@ class DISPLAY_EXPORT DisplayChangeNotifier {
  private:
   // The observers that need to be notified when a display is modified, added
   // or removed.
-  base::ObserverList<DisplayObserver>::Unchecked observer_list_;
+  base::ObserverList<DisplayObserver> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayChangeNotifier);
 };

ui/display/display_list.h

@@ -82,9 +82,7 @@ class DISPLAY_EXPORT DisplayList {
   // Removes the Display with the specified id.
   void RemoveDisplay(int64_t id);
 
-  base::ObserverList<DisplayObserver>::Unchecked* observers() {
-    return &observers_;
-  }
+  base::ObserverList<DisplayObserver>* observers() { return &observers_; }
 
  private:
   friend class DisplayListObserverLock;
@@ -101,7 +99,7 @@ class DISPLAY_EXPORT DisplayList {
 
   std::vector<Display> displays_;
   int primary_display_index_ = -1;
-  base::ObserverList<DisplayObserver>::Unchecked observers_;
+  base::ObserverList<DisplayObserver> observers_;
 
   int observer_suspend_lock_count_ = 0;
 

ui/display/display_observer.h

@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include "base/observer_list_types.h"
 #include "ui/display/display_export.h"
 
 namespace display {
@@ -15,7 +16,7 @@ class Display;
 // Observers for display configuration changes.
 // TODO(oshima): consolidate |WorkAreaWatcherObserver| and
 // |DisplaySettingsProvier|. crbug.com/122863.
-class DISPLAY_EXPORT DisplayObserver {
+class DISPLAY_EXPORT DisplayObserver : public base::CheckedObserver {
  public:
   enum DisplayMetric {
     DISPLAY_METRIC_NONE = 0,
@@ -48,7 +49,7 @@ class DISPLAY_EXPORT DisplayObserver {
                                        uint32_t changed_metrics);
 
  protected:
-  virtual ~DisplayObserver();
+  ~DisplayObserver() override;
 };
 
 }  // namespace display

ui/display/manager/display_manager.h

@@ -655,7 +655,7 @@ class DISPLAY_MANAGER_EXPORT DisplayManager
 
   base::Closure created_mirror_window_;
 
-  base::ObserverList<DisplayObserver>::Unchecked observers_;
+  base::ObserverList<DisplayObserver> observers_;
 
   // Not empty if mixed mirror mode should be turned on (the specified source
   // display is mirrored to the specified destination displays). Empty if mixed

ui/ozone/platform/scenic/scenic_screen.h

@@ -49,7 +49,7 @@ class ScenicScreen : public PlatformScreen {
 
   DisplayVector displays_;
 
-  base::ObserverList<display::DisplayObserver>::Unchecked observers_;
+  base::ObserverList<display::DisplayObserver> observers_;
 
   base::WeakPtrFactory<ScenicScreen> weak_factory_;
 

ui/ozone/platform/wayland/wayland_screen.h

@@ -50,7 +50,7 @@ class WaylandScreen : public PlatformScreen {
  private:
   display::DisplayList display_list_;
 
-  base::ObserverList<display::DisplayObserver>::Unchecked observers_;
+  base::ObserverList<display::DisplayObserver> observers_;
 
   base::WeakPtrFactory<WaylandScreen> weak_factory_;