Fix use after free for cached_displays_.

ui/ozone/demo/ozone_demo.cc

Index: ui/ozone/demo/ozone_demo.cc
diff --git a/ui/ozone/demo/ozone_demo.cc b/ui/ozone/demo/ozone_demo.cc
index bbfeff49bb96bd54dcc6a70cba85154ba30a38ab..309e36d0758b51dad29eadff3943b6257b4b2ed7 100644
--- a/ui/ozone/demo/ozone_demo.cc
+++ b/ui/ozone/demo/ozone_demo.cc
@@ -91,6 +91,7 @@ class WindowManager : public ui::NativeDisplayObserver {
 
   // ui::NativeDisplayDelegate:
   void OnConfigurationChanged() override;
+  void OnDisplaySnapshotsInvalidated() override;
 
   std::unique_ptr<ui::NativeDisplayDelegate> delegate_;
   base::Closure quit_closure_;
@@ -282,6 +283,8 @@ void WindowManager::OnConfigurationChanged() {
       base::Bind(&WindowManager::OnDisplaysAquired, base::Unretained(this)));
 }
 
+void WindowManager::OnDisplaySnapshotsInvalidated() {}
+
 void WindowManager::OnDisplaysAquired(
     const std::vector<ui::DisplaySnapshot*>& displays) {
   windows_.clear();