exo: Recreate Surface resources on context lost.

ui/views/mus/surface_context_factory.h

Index: ui/views/mus/surface_context_factory.h
diff --git a/ui/views/mus/surface_context_factory.h b/ui/views/mus/surface_context_factory.h
index c50356be4f7575d4566f159e68d054832149d057..5355168851c6d5bd4400a330f81e85c437844cb9 100644
--- a/ui/views/mus/surface_context_factory.h
+++ b/ui/views/mus/surface_context_factory.h
@@ -54,6 +54,8 @@ class VIEWS_MUS_EXPORT SurfaceContextFactory : public ui::ContextFactory {
   void SetAuthoritativeVSyncInterval(ui::Compositor* compositor,
                                      base::TimeDelta interval) override {}
   void SetOutputIsSecure(ui::Compositor* compositor, bool secure) override {}
+  void AddObserver(ui::ContextFactoryObserver* observer) override {}
+  void RemoveObserver(ui::ContextFactoryObserver* observer) override {}
 
   SurfaceBinding surface_binding_;
   uint32_t next_surface_id_namespace_;