mus: Add EventObserver to allow passively listening to UI events

components/mus/ws/test_change_tracker.cc

Index: components/mus/ws/test_change_tracker.cc
diff --git a/components/mus/ws/test_change_tracker.cc b/components/mus/ws/test_change_tracker.cc
index 7f411e682ce07722d149aa99e55d01fbd16b8d7c..065b366a44b2d453c2aad00c2c5c9955c2b6f66a 100644
--- a/components/mus/ws/test_change_tracker.cc
+++ b/components/mus/ws/test_change_tracker.cc
@@ -110,8 +110,13 @@ std::string ChangeToDescription(const Change& change,
                                 change.bool_value ? "true" : "false");
 
     case CHANGE_TYPE_INPUT_EVENT:
-      return base::StringPrintf("InputEvent window=%s event_action=%d",
-                                WindowIdToString(change.window_id).c_str(),
+      return base::StringPrintf(
+          "InputEvent window=%s event_action=%d matched_observer=%s",
+          WindowIdToString(change.window_id).c_str(), change.event_action,
+          change.bool_value ? "true" : "false");
+
+    case CHANGE_TYPE_EVENT_OBSERVED:
+      return base::StringPrintf("EventObserved event_action=%d",
                                 change.event_action);
 
     case CHANGE_TYPE_PROPERTY_CHANGED:
@@ -362,11 +367,20 @@ void TestChangeTracker::OnWindowParentDrawnStateChanged(Id window_id,
 }
 
 void TestChangeTracker::OnWindowInputEvent(Id window_id,
-                                           mojom::EventPtr event) {
+                                           mojom::EventPtr event,
+                                           bool matched_observer) {
   Change change;
   change.type = CHANGE_TYPE_INPUT_EVENT;
   change.window_id = window_id;
   change.event_action = static_cast<int32_t>(event->action);
+  change.bool_value = matched_observer;
+  AddChange(change);
+}
+
+void TestChangeTracker::OnEventObserved(mojom::EventPtr event) {
+  Change change;
+  change.type = CHANGE_TYPE_EVENT_OBSERVED;
+  change.event_action = static_cast<int32_t>(event->action);
   AddChange(change);
 }