Makes display roots be destroyed by client

services/ui/ws/window_tree_client_unittest.cc

Index: services/ui/ws/window_tree_client_unittest.cc
diff --git a/services/ui/ws/window_tree_client_unittest.cc b/services/ui/ws/window_tree_client_unittest.cc
index 507ae5226693e004bc5291bc295f1a0881e58ee3..9eff23e1f90d11cedccda23d14e8f20c04d80001 100644
--- a/services/ui/ws/window_tree_client_unittest.cc
+++ b/services/ui/ws/window_tree_client_unittest.cc
@@ -424,6 +424,7 @@ class TestWindowTreeClient : public mojom::WindowTreeClient,
                          bool drawn) override {
     NOTIMPLEMENTED();
   }
+  void WmDisplayRemoved(int64_t display_id) override { NOTIMPLEMENTED(); }
   void WmSetBounds(uint32_t change_id,
                    uint32_t window_id,
                    const gfx::Rect& bounds) override {