mus: Add UserActivityMonitor.

components/mus/ws/window_server.cc

Index: components/mus/ws/window_server.cc
diff --git a/components/mus/ws/window_server.cc b/components/mus/ws/window_server.cc
index fb6382f70af6b419a8609bba214aaa10a441d3d5..18b1cd734809bade368b1e89aafb0ce644b2b17d 100644
--- a/components/mus/ws/window_server.cc
+++ b/components/mus/ws/window_server.cc
@@ -16,6 +16,7 @@
 #include "components/mus/ws/display_manager.h"
 #include "components/mus/ws/operation.h"
 #include "components/mus/ws/server_window.h"
+#include "components/mus/ws/user_activity_monitor.h"
 #include "components/mus/ws/window_coordinate_conversions.h"
 #include "components/mus/ws/window_manager_access_policy.h"
 #include "components/mus/ws/window_manager_display_root.h"
@@ -229,6 +230,11 @@ void WindowServer::OnFirstWindowManagerWindowTreeFactoryReady() {
   delegate_->CreateDefaultDisplays();
 }
 
+UserActivityMonitor* WindowServer::GetUserActivityMonitorForUser(
+    const UserId& user_id) {
+  return GetWindowManagerStateForUser(user_id)->user_activity_monitor();
+}
+
 bool WindowServer::SetFocusedWindow(ServerWindow* window) {
   // TODO(sky): this should fail if there is modal dialog active and |window|
   // is outside that.