mus: Add EventObserver to allow passively listening to UI events

components/mus/public/cpp/lib/window_tree_client_impl.h

Index: components/mus/public/cpp/lib/window_tree_client_impl.h
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.h b/components/mus/public/cpp/lib/window_tree_client_impl.h
index 3d8d7653abedacd6236e0314a995d77a933bc8d7..3ce8301df60a787c729228d59b263d464b2ef8ee 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.h
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.h
@@ -220,7 +220,9 @@ class WindowTreeClientImpl : public WindowTreeConnection,
                                      mojo::Array<uint8_t> new_data) override;
   void OnWindowInputEvent(uint32_t event_id,
                           Id window_id,
-                          mojom::EventPtr event) override;
+                          mojom::EventPtr event,
+                          bool matched_observer) override;
+  void OnEventObserved(mojom::EventPtr event) override;
   void OnWindowFocused(Id focused_window_id) override;
   void OnWindowPredefinedCursorChanged(Id window_id,
                                        mojom::Cursor cursor) override;