Fix use after free for cached_displays_.

ui/display/types/native_display_observer.h

Index: ui/display/types/native_display_observer.h
diff --git a/ui/display/types/native_display_observer.h b/ui/display/types/native_display_observer.h
index 60910367b088a79f48fc7fdecc805c9773203b58..ba983af4f37931c40424fa85cd92e1dd37dfd55a 100644
--- a/ui/display/types/native_display_observer.h
+++ b/ui/display/types/native_display_observer.h
@@ -16,6 +16,10 @@ class DISPLAY_TYPES_EXPORT NativeDisplayObserver {
   virtual ~NativeDisplayObserver() {}
 
   virtual void OnConfigurationChanged() = 0;
+
+  // DisplaySnapshots owned by NativeDisplayDelegate are about to be
+  // invalidated and any stored pointers to them should be deleted.
+  virtual void OnDisplaySnapshotsInvalidated() = 0;
 };
 
 }  //  namespace ui