mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/ws/window_tree.cc

Index: components/mus/ws/window_tree.cc
diff --git a/components/mus/ws/window_tree.cc b/components/mus/ws/window_tree.cc
index ed05e243550eee04060839076904650c0b889b1f..5500b5512ad96f153833160757fb12bfeef16dee 100644
--- a/components/mus/ws/window_tree.cc
+++ b/components/mus/ws/window_tree.cc
@@ -18,6 +18,7 @@
 #include "components/mus/ws/platform_display.h"
 #include "components/mus/ws/server_window.h"
 #include "components/mus/ws/server_window_observer.h"
+#include "components/mus/ws/user_display_manager.h"
 #include "components/mus/ws/window_manager_state.h"
 #include "components/mus/ws/window_server.h"
 #include "components/mus/ws/window_tree_binding.h"
@@ -669,6 +670,12 @@ WindowManagerState* WindowTree::GetWindowManagerStateForWindowManager() {
   return wms;
 }
 
+void WindowTree::GetCursorScreenPoint(
+    const GetCursorScreenPointCallback& callback) {
+  callback.Run(mojo::Point::From(
+      display_manager()->GetUserDisplayManager(user_id_)->cursor_location()));
+}
+
 bool WindowTree::ShouldRouteToWindowManager(const ServerWindow* window) const {
   // If the client created this window, then do not route it through the WM.
   if (window->id().connection_id == id_)