mus: Add PointerWatcher for passively observing mouse and touch events

components/mus/demo/mus_demo.cc

Index: components/mus/demo/mus_demo.cc
diff --git a/components/mus/demo/mus_demo.cc b/components/mus/demo/mus_demo.cc
index 56dd3d45fdd7a8597f0e59a232a62b40b0765f93..cfe9bc6e2c1958227a17081e360dbb12cbb4b49d 100644
--- a/components/mus/demo/mus_demo.cc
+++ b/components/mus/demo/mus_demo.cc
@@ -90,6 +90,8 @@ void MusDemo::OnConnectionLost(mus::WindowTreeConnection* connection) {
   timer_.Stop();
 }
 
+void MusDemo::OnEventObserved(const ui::Event& event) {}
+
 void MusDemo::SetWindowManagerClient(mus::WindowManagerClient* client) {}
 
 bool MusDemo::OnWmSetBounds(mus::Window* window, gfx::Rect* bounds) {