mus: Add EventObserver to allow passively listening to UI events

components/mus/ws/test_utils.cc

Index: components/mus/ws/test_utils.cc
diff --git a/components/mus/ws/test_utils.cc b/components/mus/ws/test_utils.cc
index d1563da167dcf0f6935e49f6db02d018550994da..734f55f881515d1226a01b8ca2021d83fdf134df 100644
--- a/components/mus/ws/test_utils.cc
+++ b/components/mus/ws/test_utils.cc
@@ -109,6 +109,14 @@ PlatformDisplay* TestPlatformDisplayFactory::CreatePlatformDisplay() {
 WindowTreeTestApi::WindowTreeTestApi(WindowTree* tree) : tree_(tree) {}
 WindowTreeTestApi::~WindowTreeTestApi() {}
 
+void WindowTreeTestApi::SetEventObserver(mojom::EventMatcherPtr matcher) {
+  tree_->SetEventObserver(std::move(matcher));
+}
+
+void WindowTreeTestApi::ClearEventObserver() {
+  tree_->ClearEventObserver();
+}
+
 // DisplayTestApi  ------------------------------------------------------------
 
 DisplayTestApi::DisplayTestApi(Display* display) : display_(display) {}
@@ -259,6 +267,10 @@ void TestWindowTreeClient::OnWindowInputEvent(uint32_t event_id,
   tracker_.OnWindowInputEvent(window, std::move(event));
 }
 
+void TestWindowTreeClient::OnEventObserved(mojom::EventPtr event) {
+  tracker_.OnEventObserved(std::move(event));
+}
+
 void TestWindowTreeClient::OnWindowFocused(uint32_t focused_window_id) {
   tracker_.OnWindowFocused(focused_window_id);
 }